Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2016	$ 1,458,963	$ 1,176	$ 1,780,350	$ (322,563)
Balance (in shares) at Dec. 31, 2016		117,554
Net income	178,040			178,040
Retirement of common stock	(5,847)	$ (2)	(5,845)
Retirement of common stock (in shares)		(176)
Dividends declared on common stock	(199,764)			(199,764)
Restricted stock compensation, net of forfeitures	13,286		13,286
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		513
Stock options exercised	6,930	$ 3	6,927
Stock options exercised (in shares)		313
Balance at Dec. 31, 2017	1,451,608	$ 1,182	1,794,713	(344,287)
Balance (in shares) at Dec. 31, 2017		118,204
Net income	159,207			159,207
Retirement of common stock	(3,005)	$ (1)	(3,004)
Retirement of common stock (in shares)		(139)
Dividends declared on common stock	(205,675)			(205,675)
Restricted stock compensation, net of forfeitures	13,132		13,132
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		462
Stock options exercised	2,367	$ 1	2,366
Stock options exercised (in shares)		147
Cumulative effect of adoption of new accounting standard	(2,575)			(2,575)
Balance at Dec. 31, 2018	1,415,059	$ 1,187	1,807,202	(393,330)
Balance (in shares) at Dec. 31, 2018		118,674
Net income	188,886			188,886
Retirement of common stock	(3,531)	$ (2)	(3,529)
Retirement of common stock (in shares)		(164)
Dividends declared on common stock	(211,868)			(211,868)
Restricted stock compensation, net of forfeitures	17,267		17,267
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		524
Stock options exercised	876	$ 1	875
Stock options exercised (in shares)		62
Cumulative effect of adoption of new accounting standard	(29,940)			(29,940)
Balance at Dec. 31, 2019	$ 1,376,749	$ 1,191	$ 1,821,810	$ (446,252)
Balance (in shares) at Dec. 31, 2019		119,096