Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Private Placement	Public offering	Common Shares	Common Shares Public offering	Additional Paid-In Capital	Additional Paid-In Capital Private Placement	Additional Paid-In Capital Public offering	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Accumulated Deficit)	Treasury Stock	Class A Common Shares Common Shares	Class A Common Shares Common Shares Private Placement	Class B-2 Common Shares Common Shares
Balance, beginning of period at Dec. 31, 2012	$ 219,123			$ 0		$ 347,924			$ 2,414	$ (97,512)	$ (34,142)	$ 348		$ 91
Changes in Stockholders' Equity
Net income	65,413									65,413
Other comprehensive income (loss)	(3,861)								(3,861)
Issuance of common shares net of issuance cost		$ 123,852	$ 313,713		$ 299		$ 123,729	$ 313,414					$ 123
Conversion of Class A and Class B-2 shares into Common Shares				1,004		(476)						(474)		(54)
Issuance of management incentive shares	615			28		582						3		2
Forfeiture of management incentive shares						39								(39)
Stock-based compensation expense	3,597					3,597
Treasury stock acquired	(311)										(311)
Cancellation of treasury stock				(34)		(34,419)					34,453
Balance, end of period at Dec. 31, 2013	722,141			1,297		754,390			(1,447)	(32,099)	0	$ 0		$ 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			$ 126,739		$ 90			$ 126,649
Issuance of management incentive shares	416			2		414
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				(1)		(2,497)					2,498
Balance, end of period at Dec. 31, 2014	955,738			1,388		893,285			4,667	56,398
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, end of period at Dec. 31, 2015	$ 1,119,241			$ 1,390		$ 904,221			$ (99)	$ 213,729