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Stock Based Compensation (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Feb. 16, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jun. 10, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Maximum shares of common stock provided (in shares)         8,700,000
Fair value of stock option awards outstanding (in shares)   3,064,000 2,887,000    
Aggregate intrinsic value   $ 30,600      
Aggregate intrinsic value exercisable   $ 8,500      
Quoted closing market price   $ 31.13      
Weighted average contractual term   1 year 25 days      
Total intrinsic value of options exercised   $ 13,200 $ 1,600 $ 1,300  
Tax related benefits realized from the exercise of stock options   5,000 500 300  
Unrecognized compensation expense related to unvested stock options   $ 9,800      
Weighted average remaining requisite service period of unvested stock awards   9 months 12 days      
Fair value of option shares vested   $ 2,100 3,000 1,300  
Stock-based compensation expense   16,654 12,362 9,450  
Stock based long term liability   400 1,400 0  
Stock based current liability   $ 0 0 1,000  
Restricted stock or unit expenses       0  
Options granted (in shares)   1,034,000      
Aggregate intrinsic value for the restricted stock and restricted stock units outstanding   $ 36,400      
Tax benefits recognized for stock based compensation   6,800 4,300 3,400  
Capitalized stock-based compensation   3,300      
Expensed stock-based compensation   $ 16,700      
Minimum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period of shares   3 years      
Maximum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period of shares   4 years      
Class A [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Maximum shares that may be issued pursuant to options or restricted stock grants (in shares)   3,481,569      
Restricted stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Weighted average remaining requisite service period of unvested stock awards   11 months 12 days      
Unrecognized compensation expense related to unvested restricted stock and restricted stock units   $ 14,400      
Fair value of restricted stock and restricted stock units vested   9,900 4,600 800  
Restricted stock or unit expenses   $ 12,900 6,600 4,700  
Stock options [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Maximum vesting period   5 years      
Maximum vesting period 2   6 years      
Maximum vesting period 3   10 years      
Stock-based compensation expense   $ 7,100 $ 5,900 $ 4,700  
Subsequent Event [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted (in shares) 563,408        
Fair value of grants $ 26,900        
Subsequent Event [Member] | Restricted stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock grants (in shares) 667,488        
Subsequent Event [Member] | Stock options [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period of shares 3 years        
Weighted average fair value, Granted $ 29.68        
2003 Stock and Incentive Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Fair value of stock option awards outstanding (in shares)   75,000 77,500 87,500