CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock and Paid in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, beginning of the period (in shares) at Dec. 31, 2015		34,242,255
Balance, beginning of the period at Dec. 31, 2015	$ 1,300,059		$ 1,261,174	$ 39,615	$ (730)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	85,385			85,385
Other comprehensive income, net of income tax	(2,725)				(2,725)
Accrual of dividends on common stock	(29,672)			(29,672)
Proceeds from issuance of common stock for stockholder reinvestment program (in shares)		96,382
Repurchase of common stock under the terms of the repurchase plan (in shares)		(1,145,250)
Stock Repurchased and Retired During Period, Value	(50,772)		(50,772)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	3,401		3,401
Excess tax benefit on stock-based compensation	34		34
Balance, end of the period (in shares) at Dec. 31, 2016		33,193,387
Balance, end of the period at Dec. 31, 2016	1,305,710		1,213,837	95,328	(3,455)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,793			23,793
Other comprehensive income, net of income tax	1,559				1,559
Accrual of dividends on common stock	(8,338)			(8,338)
Amortization of compensation related to restricted stock grant shares		(40,523)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	680		680
Balance, end of the period (in shares) at Mar. 31, 2017		33,152,864
Balance, end of the period at Mar. 31, 2017	$ 1,323,404		$ 1,214,517	$ 110,783	$ (1,896)