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	47,951
Other comprehensive (loss) income	13,359
Stockholders equity, end of period at Mar. 31, 2016				13,260
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
Changes in Stockholders' Equity
Net income	66,598				66,598
Other comprehensive (loss) income	4,850			4,850
Issuance of management incentive shares	0	7	(7)
Stock-based compensation expense	4,619		4,619
Treasury stock acquired	(7,127)					(7,127)
Cancellation of treasury stock	0	(3)	(7,124)			7,127
Stockholders equity, end of period at Mar. 31, 2017	1,412,752	$ 1,401	915,895	$ (7,405)	502,861	$ 0
Changes in Stockholders' Equity
Cumulative effect of ASU 2016-09 adoption	$ 39		$ 111		$ (72)