Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Details)

v3.19.3.a.u2
Stockholders' Equity - Additional Information (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Jun. 20, 2013
shares
Dec. 31, 2019
USD ($)
director
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2006
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of directors | director   1      
Granted (in dollars per share) | $ / shares   $ 110.56 $ 64.11 $ 48.52  
Total unrecognized compensation cost related to nonvested shares of common stock granted | $   $ 26.5      
Weighted average period of cost recognized   3 years 25 days      
Fair value of shares vested | $   $ 9.4 $ 8.0 $ 5.6  
Compensation expense related to nonvested stock grants | $   $ 9.6 $ 9.4 $ 6.0  
Price of shares issued under employee stock purchase plan as a percentage of FMV         95.00%
Number of shares reserved for the employee stock purchase plan (in shares)         250,000
Additional shares authorized for issuance (in shares) 250,000        
Shares redeemed to satisfy personal tax obligations (in shares)   107,461 138,925 61,825  
Director          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Period of vested shares   1 year      
Nonvested stock grants to employees (in shares)   3,500      
Nonvested stock grants to Independent directors (in shares)   17,880 13,600 11,700  
New Director          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of directors' stock grant vested on one year anniversary date   33.33%      
Employee          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Period of vested shares   5 years      
2018 Long-Term Incentive Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Common stock reserved and available for issuance (in shares)     2,210,544    
Shares available for issuance (in shares)     2,009,444    
2018 Long-Term Incentive Plan | Employee          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Nonvested stock grants to employees (in shares)   163,250      
2010 Long-Term Incentive Plan | Employee          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Nonvested stock grants to employees (in shares)     213,105 139,310  
Nonvested stock          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Aggregate intrinsic value, outstanding | $   $ 5.5      
Aggregate intrinsic value, exercised | $   $ 1.5