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, 2014	$ 955,738	$ 1,388	$ 893,285	$ 4,667	$ 56,398	$ 0
Changes in Stockholders' Equity
Net income	72,031
Other comprehensive income (loss)	(3,880)
Stockholders equity, end of period at Jun. 30, 2015				787
Stockholders equity, beginning of period at Dec. 31, 2014	955,738	1,388	893,285	4,667	56,398	0
Changes in Stockholders' Equity
Net income	157,331				157,331
Other comprehensive income (loss)	(4,766)			(4,766)
Issuance of management incentive shares		6	(6)
Forfeiture of management incentive shares		(1)	1
Stock-based compensation expense	13,633		13,633
Excess tax benefits from stock-based compensation expense	2,420		2,420
Treasury stock acquired	(5,168)					(5,168)
Cancellation of treasury stock		(3)	(5,165)			5,168
Other equity transactions	53		53
Stockholders equity, end of period at Dec. 31, 2015	1,119,241	1,390	904,221	(99)	213,729	0
Stockholders equity, beginning of period at Mar. 31, 2015				9,556
Changes in Stockholders' Equity
Net income	37,193
Other comprehensive income (loss)	(8,769)
Stockholders equity, end of period at Jun. 30, 2015				787
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				100,209
Other comprehensive income (loss)	24,061			24,061
Issuance of management incentive shares		10	(10)
Stock-based compensation expense	7,949		7,949
Excess tax benefits from stock-based compensation expense	1,023		1,023
Treasury stock acquired	(3,876)					(3,876)
Cancellation of treasury stock		(3)	(3,873)			3,876
Stockholders equity, end of period at Jun. 30, 2016	1,248,607	1,397	909,310	23,962	313,938	0
Stockholders equity, beginning of period at Mar. 31, 2016				13,260
Changes in Stockholders' Equity
Net income	52,258
Other comprehensive income (loss)	10,702
Stockholders equity, end of period at Jun. 30, 2016	$ 1,248,607	$ 1,397	$ 909,310	$ 23,962	$ 313,938	$ 0