Net Earnings Per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) item $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares
Numerator
Net income | $	$ 91,803	$ 76,118	$ 184,661	$ 95,450
Denominator
Weighted-average common shares outstanding	102,837,443	102,571,600	102,758,427	102,513,642
Basic net income per share (in dollars per share) | $ / shares	$ 0.89	$ 0.74	$ 1.80	$ 0.93
Numerator
Net income | $	$ 91,803	$ 76,118	$ 184,661	$ 95,450
Assumed conversion of convertible senior notes | $	1,455	1,446	2,909	2,877
Net income plus assumed conversions | $	$ 93,258	$ 77,564	$ 187,570	$ 98,327
Denominator
Number of shares used in basic computation	102,837,443	102,571,600	102,758,427	102,513,642
Weighted-average effect of dilutive securities (in shares)	8,001,737	8,166,244	7,951,747	8,131,672
Number of shares used in per share computation	110,839,180	110,737,844	110,710,174	110,645,314
Diluted net income per share (in dollars per share) | $ / shares	$ 0.84	$ 0.70	$ 1.69	$ 0.89
Number of classes of common stock | item			2
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted earnings per share (in shares)		982,769	1,006,647