Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common stock	Other paid-in capital	Retained earnings	Accumulated other comprehensive loss	Treasury stock
Cumulative effect of adoption of ASU 2014-09 | Accounting Standards Update 2014-09	$ (970)			$ (970)
Balance (in shares) at Dec. 31, 2017		195,843,297
Treasury stock (in shares) at Dec. 31, 2017						(538,921)
Balance at Dec. 31, 2017	2,429,043	$ 195,843	$ 1,233,412	1,040,748	$ (37,334)	$ (3,626)
Balance (Accounting Standards Update 2014-09) at Dec. 31, 2017	2,428,073			1,039,778
Net income	42,437			42,437
Other comprehensive income	433				433
Reclassification of certain prior period tax effects from accumulated other comprehensive loss | Adjustments for new accounting pronouncement	0			7,959	(7,959)
Dividends declared on common stock	(38,705)			(38,705)
Stock-based compensation	1,223		1,223
Repurchase of common stock						(182,424)
Repurchase of common stock	(5,020)					$ (5,020)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(7,350)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)						182,424
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings						$ 5,020
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(2,330)
Balance (in shares) at Mar. 31, 2018		195,843,297
Treasury stock (in shares) at Mar. 31, 2018						(538,921)
Balance at Mar. 31, 2018	2,426,111	$ 195,843	1,227,285	1,051,469	(44,860)	$ (3,626)
Balance (in shares) at Dec. 31, 2017		195,843,297
Treasury stock (in shares) at Dec. 31, 2017						(538,921)
Balance at Dec. 31, 2017	2,429,043	$ 195,843	1,233,412	1,040,748	(37,334)	$ (3,626)
Balance (Accounting Standards Update 2014-09) at Dec. 31, 2017	2,428,073			1,039,778
Net income	193,490
Other comprehensive income	1,674
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (2,330)
Balance (in shares) at Sep. 30, 2018	196,557,245	196,557,245
Treasury stock (in shares) at Sep. 30, 2018						(538,921)
Balance at Sep. 30, 2018	$ 2,521,293	$ 196,557	1,247,151	1,124,830	(43,619)	$ (3,626)
Balance (in shares) at Mar. 31, 2018		195,843,297
Treasury stock (in shares) at Mar. 31, 2018						(538,921)
Balance at Mar. 31, 2018	2,426,111	$ 195,843	1,227,285	1,051,469	(44,860)	$ (3,626)
Net income	43,802			43,802
Other comprehensive income	725				725
Dividends declared on common stock	(38,847)			(38,847)
Stock-based compensation	1,294		1,294
Issuance of common stock (shares)		713,948
Issuance of common stock	17,993	$ 714	17,279
Balance (in shares) at Jun. 30, 2018		196,557,245
Treasury stock (in shares) at Jun. 30, 2018						(538,921)
Balance at Jun. 30, 2018	2,451,078	$ 196,557	1,245,858	1,056,424	(44,135)	$ (3,626)
Net income	107,251			107,251
Other comprehensive income	516				516
Dividends declared on common stock	(38,845)			(38,845)
Stock-based compensation	$ 1,293		1,293
Balance (in shares) at Sep. 30, 2018	196,557,245	196,557,245
Treasury stock (in shares) at Sep. 30, 2018						(538,921)
Balance at Sep. 30, 2018	$ 2,521,293	$ 196,557	1,247,151	1,124,830	(43,619)	$ (3,626)
Balance (in shares) at Dec. 31, 2018	196,564,907	196,564,907
Treasury stock (in shares) at Dec. 31, 2018						(538,921)
Balance at Dec. 31, 2018	$ 2,566,775	$ 196,565	1,248,576	1,163,602	(38,342)	$ (3,626)
Net income	40,926			40,926
Other comprehensive income	774				774
Dividends declared on common stock	(40,019)			(40,019)
Stock-based compensation	1,617		1,617
Share Based Compensation, Shares, Shares Issued Net Of Tax Withholdings		246,214
Share Based Compensation Value Issued Shares Net Of Tax Withholdings		$ 246
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(3,261)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(3,015)
Issuance of common stock (shares)		1,505,687
Issuance of common stock	38,634	$ 1,506	37,128
Balance (in shares) at Mar. 31, 2019		198,316,808
Treasury stock (in shares) at Mar. 31, 2019						(538,921)
Balance at Mar. 31, 2019	$ 2,605,692	$ 198,317	1,284,060	1,164,509	(37,568)	$ (3,626)
Balance (in shares) at Dec. 31, 2018	196,564,907	196,564,907
Treasury stock (in shares) at Dec. 31, 2018						(538,921)
Balance at Dec. 31, 2018	$ 2,566,775	$ 196,565	1,248,576	1,163,602	(38,342)	$ (3,626)
Net income	240,388
Other comprehensive income	1,664
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (3,015)
Balance (in shares) at Sep. 30, 2019	200,876,334	200,876,334
Treasury stock (in shares) at Sep. 30, 2019						(538,921)
Balance at Sep. 30, 2019	$ 2,795,606	$ 200,876	1,351,990	1,283,044	(36,678)	$ (3,626)
Balance (in shares) at Mar. 31, 2019		198,316,808
Treasury stock (in shares) at Mar. 31, 2019						(538,921)
Balance at Mar. 31, 2019	2,605,692	$ 198,317	1,284,060	1,164,509	(37,568)	$ (3,626)
Net income	61,825			61,825
Other comprehensive income	478				478
Dividends declared on common stock	(40,367)			(40,367)
Stock-based compensation	1,742		1,742
Issuance of common stock (shares)		1,222,302
Issuance of common stock	30,931	$ 1,222	29,709
Balance (in shares) at Jun. 30, 2019		199,539,110
Treasury stock (in shares) at Jun. 30, 2019						(538,921)
Balance at Jun. 30, 2019	2,660,301	$ 199,539	1,315,511	1,185,967	(37,090)	$ (3,626)
Net income	137,637			137,637
Other comprehensive income	412				412
Dividends declared on common stock	(40,560)			(40,560)
Stock-based compensation	1,742		1,742
Issuance of common stock (shares)		1,337,224
Issuance of common stock	$ 36,074	$ 1,337	34,737
Balance (in shares) at Sep. 30, 2019	200,876,334	200,876,334
Treasury stock (in shares) at Sep. 30, 2019						(538,921)
Balance at Sep. 30, 2019	$ 2,795,606	$ 200,876	$ 1,351,990	$ 1,283,044	$ (36,678)	$ (3,626)