Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Stockholders equity, beginning of period at Dec. 31, 2015	$ 1,119,241	$ 1,390	$ 904,221	$ (99)	$ 213,729	$ 0
Changes in Stockholders' Equity
Net income	100,209
Other comprehensive (loss) income	24,061
Stockholders equity, end of period at Jun. 30, 2016				23,962
Stockholders equity, beginning of period at Dec. 31, 2015	1,119,241	1,390	904,221	(99)	213,729	0
Changes in Stockholders' Equity
Net income	222,606				222,606
Other comprehensive (loss) income	(12,156)			(12,156)
Issuance of management incentive shares	0	10	(10)
Forfeiture of management incentive shares	0	0	0
Stock-based compensation expense	16,881		16,881
Excess tax benefits from stock-based compensation expense	1,083		1,083
Treasury stock acquired	(4,024)					(4,024)
Cancellation of treasury stock	0	(3)	(4,021)			4,024
Other equity transactions	142		142
Stockholders equity, end of period at Dec. 31, 2016	1,343,773	1,397	918,296	(12,255)	436,335	0
Stockholders equity, beginning of period at Mar. 31, 2016				13,260
Changes in Stockholders' Equity
Net income	52,258
Other comprehensive (loss) income	10,702
Stockholders equity, end of period at Jun. 30, 2016				23,962
Changes in Stockholders' Equity
Cumulative effect of ASU 2016-09 adoption	39		111		(72)
Stockholders equity, beginning of period at Dec. 31, 2016	1,343,773	1,397	918,296	(12,255)	436,335	0
Changes in Stockholders' Equity
Net income	138,716				138,716
Other comprehensive (loss) income	13,320			13,320
Issuance of management incentive shares	0	8	(8)
Stock-based compensation expense	9,288		9,288
Treasury stock acquired	(7,239)					(7,239)
Cancellation of treasury stock	0	(4)	(7,235)			7,239
Stockholders equity, end of period at Jun. 30, 2017	1,497,897	1,401	920,452	1,065	574,979	0
Stockholders equity, beginning of period at Mar. 31, 2017				(7,405)
Changes in Stockholders' Equity
Net income	72,118
Other comprehensive (loss) income	8,470
Stockholders equity, end of period at Jun. 30, 2017	$ 1,497,897	$ 1,401	$ 920,452	$ 1,065	$ 574,979	$ 0