Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Retained Earnings
Beginning balance, shares at Dec. 31, 2014		57,192,212
Beginning balance at Dec. 31, 2014	$ 1,326,911	$ 572	$ 1,227,091	$ 99,248
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, including stock option exercises, shares		33,868
Issuance of common stock, including stock option exercises	110	$ 0	110
Repurchases of common stock, shares		(1,645,075)
Repurchases of common stock	(24,983)	$ (16)	(24,967)
Dividends on common stock	(103,860)			(103,860)
Share-based compensation	184		184
Net income (loss)	(46,005)			(46,005)
Ending balance, shares at Dec. 31, 2015		55,581,005
Ending balance at Dec. 31, 2015	1,152,357	$ 556	1,202,418	(50,617)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, including stock option exercises, shares		44,995
Issuance of common stock, including stock option exercises	59	$ 1	58
Repurchases of common stock, shares		(1,958,369)
Repurchases of common stock	(21,538)	$ (20)	(21,518)
Dividends on common stock	(41,069)			(41,069)
Share-based compensation	1,287		1,287
Net income (loss)	$ (228,028)			(228,028)
Ending balance, shares at Dec. 31, 2016	53,667,631	53,667,631
Ending balance at Dec. 31, 2016	$ 863,068	$ 537	1,182,245	(319,714)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, including stock option exercises, shares		150,613
Issuance of common stock, including stock option exercises	105	$ 1	104
Repurchases of common stock, shares		(370,294)
Repurchases of common stock	(5,165)	$ (4)	(5,161)
Dividends on common stock	(32,091)			(32,091)
Share-based compensation	4,139		4,139
Net income (loss)	$ (185,454)			(185,454)
Ending balance, shares at Dec. 31, 2017	53,447,950	53,447,950
Ending balance at Dec. 31, 2017	$ 644,602	$ 534	$ 1,181,327	$ (537,259)