Net Earnings Per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) item $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares
Numerator
Net income | $	$ 93,276	$ 77,042	$ 277,937	$ 172,492
Denominator
Weighted-average common shares outstanding	102,842,996	102,580,955	102,786,822	102,536,326
Basic net income per share (in dollars per share) | $ / shares	$ 0.91	$ 0.75	$ 2.70	$ 1.68
Numerator
Net income | $	$ 93,276	$ 77,042	$ 277,937	$ 172,492
Assumed conversion of convertible senior notes | $	1,472	1,463	4,382	4,341
Net income plus assumed conversions | $	$ 94,748	$ 78,505	$ 282,319	$ 176,833
Denominator
Number of shares used in basic computation	102,842,996	102,580,955	102,786,822	102,536,326
Weighted-average effect of dilutive securities (in shares)	7,945,917	8,043,005	7,951,067	8,098,956
Number of shares used in per share computation	110,788,913	110,623,960	110,737,889	110,635,282
Diluted net income per share (in dollars per share) | $ / shares	$ 0.86	$ 0.71	$ 2.55	$ 1.60
Number of classes of common stock | item			2
Employee and Directors Stock Options
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted earnings per share (in shares)	150,000
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted earnings per share (in shares)		947,643	994,001