Consolidated Statement of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2017	$ 1,451,608	$ 1,182	$ 1,794,713	$ (344,287)
Balance (in shares) at Dec. 31, 2017		118,204
Comprehensive income
Net income	37,777			37,777
Change in fair value of interest rate swap, net of tax	(2,028)				$ (2,028)
Total comprehensive income	35,749			37,777	(2,028)
Retirement of common stock	(2,525)	$ (1)	(2,524)
Retirement of common stock (in shares)		(117)
Dividends declared on common stock	(51,533)			(51,533)
Restricted stock compensation, net of forfeitures	3,486		3,486
Restricted stock grants		$ 4	(4)
Restricted stock grants (in shares)		457
Cumulative effect of adoption of new accounting standard	(2,575)			(2,575)
Balance at Mar. 31, 2018	1,434,210	$ 1,185	1,795,671	(360,618)	(2,028)
Balance (in shares) at Mar. 31, 2018		118,544
Balance at Dec. 31, 2017	1,451,608	$ 1,182	1,794,713	(344,287)
Balance (in shares) at Dec. 31, 2017		118,204
Comprehensive income
Net income	76,974
Balance at Jun. 30, 2018	1,427,918	$ 1,185	1,799,632	(372,899)
Balance (in shares) at Jun. 30, 2018		118,548
Balance at Mar. 31, 2018	1,434,210	$ 1,185	1,795,671	(360,618)	(2,028)
Balance (in shares) at Mar. 31, 2018		118,544
Comprehensive income
Net income	39,197			39,197
Change in fair value of interest rate swap, net of tax	2,028				2,028
Total comprehensive income	41,225			39,197	$ 2,028
Retirement of common stock	(19)		(19)
Retirement of common stock (in shares)		(1)
Dividends declared on common stock	(51,478)			(51,478)
Restricted stock compensation, net of forfeitures	3,980		3,980
Restricted stock grants (in shares)		5
Balance at Jun. 30, 2018	1,427,918	$ 1,185	1,799,632	(372,899)
Balance (in shares) at Jun. 30, 2018		118,548
Balance at Dec. 31, 2018	1,415,059	$ 1,187	1,807,202	(393,330)
Balance (in shares) at Dec. 31, 2018		118,674
Comprehensive income
Net income	49,340			49,340
Retirement of common stock	(3,070)	$ (1)	(3,069)
Retirement of common stock (in shares)		(143)
Dividends declared on common stock	(52,994)			(52,994)
Restricted stock compensation, net of forfeitures	3,812		3,812
Restricted stock grants		$ 5	(5)
Restricted stock grants (in shares)		521
Stock options exercised	207		207
Stock options exercised ( in shares)		16
Cumulative effect of adoption of new accounting standard	(29,940)			(29,940)
Balance at Mar. 31, 2019	1,382,414	$ 1,191	1,808,147	(426,924)
Balance (in shares) at Mar. 31, 2019		119,068
Balance at Dec. 31, 2018	1,415,059	$ 1,187	1,807,202	(393,330)
Balance (in shares) at Dec. 31, 2018		118,674
Comprehensive income
Net income	97,918
Balance at Jun. 30, 2019	1,382,591	$ 1,191	1,812,611	(431,211)
Balance (in shares) at Jun. 30, 2019		119,096
Balance at Mar. 31, 2019	1,382,414	$ 1,191	1,808,147	(426,924)
Balance (in shares) at Mar. 31, 2019		119,068
Comprehensive income
Net income	48,578			48,578
Retirement of common stock	(460)		(460)
Retirement of common stock (in shares)		(21)
Dividends declared on common stock	(52,865)			(52,865)
Restricted stock compensation, net of forfeitures	4,256		4,256
Restricted stock grants (in shares)		3
Stock options exercised	668		668
Stock options exercised ( in shares)		46
Balance at Jun. 30, 2019	$ 1,382,591	$ 1,191	$ 1,812,611	$ (431,211)
Balance (in shares) at Jun. 30, 2019		119,096