Net Income per Common Share (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Net income $ 21,557 $ 24,853
Weighted-average shares of common stock used to compute basic net income per share (excluding unvested restricted stock) (shares) 105,928 109,164
Weighted Average Number Diluted Shares Outstanding Adjustment [Abstract]    
Shares used in computing diluted net income per common share (shares) 107,424 111,935
Basic net income per common share (usd per share) $ 0.20 $ 0.23
Diluted net income per common share (usd per share) $ 0.20 $ 0.22
Weighted average stock options and restricted stock units excluded from calculation due to anti-dilutive effect (shares) 3,898 4,653
Restricted Stock Units (RSUs) [Member]    
Weighted Average Number Diluted Shares Outstanding Adjustment [Abstract]    
Dilutive effect of incremental common shares (shares) 928 654
Option Grants [Member]    
Weighted Average Number Diluted Shares Outstanding Adjustment [Abstract]    
Dilutive effect of incremental common shares (shares) 568 2,117