Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance 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
Balance at Dec. 31, 2015	1,119,241	1,390	904,221	(99)	213,729
Changes in Stockholders' Equity
Net income	47,951				47,951
Other comprehensive income (loss)	13,359			13,359
Issuance of management incentive shares		9	(9)
Forfeiture of management incentive shares		0	0
Stock-based compensation expense	3,782		3,782
Excess tax benefits from stock-based compensation expense	1,005		1,005
Treasury stock acquired	(3,843)					(3,843)
Cancellation of treasury stock		(3)	(3,840)			$ 3,843
Balance at Mar. 31, 2016	$ 1,181,495	$ 1,396	$ 905,159	$ 13,260	$ 261,680