Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Public offering	Common Shares	Common Shares Public offering	Additional Paid-In Capital	Additional Paid-In Capital Public offering	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Accumulated Deficit)	Treasury Stock
Stockholders equity, beginning of period at Dec. 31, 2013	$ 722,141		$ 1,297		$ 754,390		$ (1,447)	$ (32,099)	$ 0
Changes in Stockholders' Equity
Net income	88,497							88,497
Other comprehensive income (loss)	6,114						6,114
Issuance of Common Shares net of issuance cost of $6,761		$ 126,739		$ 90		$ 126,649
Issuance of management incentive shares	416		2		414
Forfeiture of management incentive shares	0		0		0
Stock-based compensation expense	12,520				12,520
Excess tax benefits from stock-based compensation expense	1,809				1,809
Treasury stock acquired	(2,498)								(2,498)
Cancellation of treasury stock	0		(1)		(2,497)				2,498
Stockholders equity, end 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	0		6		(6)
Forfeiture of management incentive shares	0		(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	0		(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
Changes in Stockholders' Equity
Net income	222,606							222,606
Other comprehensive income (loss)	(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