Condensed Consolidated Statements of Stockholders' Equity (UNAUDITED) - USD ($)		Total		Common Stock	Additional Paid-in Capital	Accumulated Retained Earnings
Beginning balance, value at Dec. 31, 2017		$ 518,000,000		$ 1,000,000	$ 162,000,000	$ 355,000,000
Beginning balance, shares at Dec. 31, 2017				99,000,000
Net income		30,000,000		$ 0	0	30,000,000
Activity related to share-based compensation		(1,000,000)		0	(1,000,000)	0
Repurchase and retirement of common stock		(112,000,000)		$ 0	(3,000,000)	(109,000,000)
Repurchase and retirement of common stock, shares				(2,000,000)
Revenue recognition cumulative-effect adjustment		(38,000,000)		$ 0	0	(38,000,000)
Capital contribution		3,000,000		0	3,000,000	0
Ending balance, value at Mar. 31, 2018		400,000,000		$ 1,000,000	161,000,000	238,000,000
Ending balance, shares at Mar. 31, 2018				97,000,000
Beginning balance, value at Dec. 31, 2017		518,000,000		$ 1,000,000	162,000,000	355,000,000
Beginning balance, shares at Dec. 31, 2017				99,000,000
Net income	[1]	177,564,538
Ending balance, value at Sep. 30, 2018		562,000,000		$ 1,000,000	174,000,000	387,000,000
Ending balance, shares at Sep. 30, 2018				97,000,000
Beginning balance, value at Mar. 31, 2018		400,000,000		$ 1,000,000	161,000,000	238,000,000
Beginning balance, shares at Mar. 31, 2018				97,000,000
Net income		107,000,000		$ 0	0	107,000,000
Activity related to share-based compensation		6,000,000		0	6,000,000	0
Other		4,000,000		0	3,000,000	1,000,000
Ending balance, value at Jun. 30, 2018		517,000,000		$ 1,000,000	170,000,000	346,000,000
Ending balance, shares at Jun. 30, 2018				97,000,000
Net income		40,533,279	[1]	$ 0	0	41,000,000
Activity related to share-based compensation		4,000,000		0	4,000,000	0
Ending balance, value at Sep. 30, 2018		562,000,000		$ 1,000,000	174,000,000	387,000,000
Ending balance, shares at Sep. 30, 2018				97,000,000
Beginning balance, value at Dec. 31, 2018		$ 616,000,000		$ 1,000,000	174,000,000	441,000,000
Beginning balance, shares at Dec. 31, 2018		94,558,086		94,000,000
Net income		$ 55,000,000		$ 0	0	55,000,000
Activity related to share-based compensation		1,000,000		0	1,000,000	0
Repurchase and retirement of common stock		(97,000,000)		$ 0	(5,000,000)	(92,000,000)
Repurchase and retirement of common stock, shares				(3,000,000)
Ending balance, value at Mar. 31, 2019		575,000,000		$ 1,000,000	170,000,000	404,000,000
Ending balance, shares at Mar. 31, 2019				91,000,000
Beginning balance, value at Dec. 31, 2018		$ 616,000,000		$ 1,000,000	174,000,000	441,000,000
Beginning balance, shares at Dec. 31, 2018		94,558,086		94,000,000
Net income	[1]	$ 144,352,584
Ending balance, value at Sep. 30, 2019		$ 494,000,000		$ 1,000,000	174,000,000	319,000,000
Ending balance, shares at Sep. 30, 2019		85,469,804		85,000,000
Beginning balance, value at Mar. 31, 2019		$ 575,000,000		$ 1,000,000	170,000,000	404,000,000
Beginning balance, shares at Mar. 31, 2019				91,000,000
Net income		39,000,000		$ 0	0	39,000,000
Activity related to share-based compensation		10,000,000		0	10,000,000	0
Repurchase and retirement of common stock		(174,000,000)		$ 0	(11,000,000)	(163,000,000)
Repurchase and retirement of common stock, shares				(5,000,000)
Ending balance, value at Jun. 30, 2019		450,000,000		$ 1,000,000	169,000,000	280,000,000
Ending balance, shares at Jun. 30, 2019				86,000,000
Net income		50,000,000	[1]	$ 0	0	50,000,000
Activity related to share-based compensation		6,000,000		0	6,000,000	0
Repurchase and retirement of common stock		(12,000,000)		$ 0	(1,000,000)	(11,000,000)
Repurchase and retirement of common stock, shares				(1,000,000)
Ending balance, value at Sep. 30, 2019		$ 494,000,000		$ 1,000,000	$ 174,000,000	$ 319,000,000
Ending balance, shares at Sep. 30, 2019		85,469,804		85,000,000

[1] Net income for the three months ended September 30, 2019 and 2018 was $50,659,927 and $40,533,279, respectively, and for the nine months ended September 30, 2019