XML 67 R56.htm IDEA: XBRL DOCUMENT v3.8.0.1
Employee Benefits and Share-Based Compensation - Stock Option Activity (Details) - 2009 Plan - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Number of Shares      
Outstanding at beginning of period (in shares) 3,323    
Granted (in shares) 482    
Exercised (in shares) (87)    
Expired (in shares) (1)    
Forfeited (in shares) (43)    
Outstanding at end of period (in shares) 3,674   3,323
Exercisable at end of period (in shares) 1,474    
Vested and expected to vest at end of period (in shares) 3,456    
Weighted Average Exercise Price      
Outstanding beginning balance (in dollars per share) $ 32.72    
Granted (in dollars per share) 44.38    
Exercised (in dollars per share) 22.50    
Expired (in dollars per share) 24.09    
Forfeited (in dollars per share) 37.14    
Outstanding ending balance (in dollars per share) 34.45   $ 32.72
Exercisable at end of period (in dollars per share) 25.36    
Vested and expected to vest at end of period (in dollars per share) $ 33.94    
Weighted-average remaining years, outstanding 7 years 3 months 11 days   7 years 7 months 13 days
Weighted-average remaining years, exercisable at end of period 5 years 4 months 6 days    
Weighted-average remaining years, vested and expected to vest at at end of period 7 years 2 months 9 days    
Aggregate Intrinsic Value      
Aggregate intrinsic value, outstanding at end of period $ 37,607   $ 53,953
Aggregate intrinsic value, exercisable at end of period 26,596    
Aggregate intrinsic value, vested and expected to vest at end of period $ 36,818    
Employee Stock Option      
Aggregate Intrinsic Value      
Weighted-average fair value (in dollars per share) $ 14.22 $ 10.86  
Intrinsic value of options exercised $ 2,000 $ 2,900  
Unrecognized compensation cost of unvested stock options   $ 23,100  
Weighted average period of compensation cost not yet recognized (in years) 3 years