Statements of Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings/ (Accumulated Deficit)	Accumulated Other Comprehensive Income (loss)	Total Equity
Beginning Balance at Dec. 31, 2016		$ 2,500	$ 8,095,436	$ (693,258)	$ (314,948)	$ 7,089,730
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital			(950,000)			(950,000)
Comprehensive income:
Net income (loss)	$ (83,504)			(83,504)		(83,504)
Other comprehensive income (loss), net of tax	224,824				224,824	224,824
Total comprehensive income (loss)						141,320
Ending Balance at Dec. 31, 2017		2,500	7,145,436	(776,762)	(90,124)	6,281,050
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital			(1,025,000)			(1,025,000)
Comprehensive income:
Net income (loss)	1,682,716			1,682,716		1,682,716
Other comprehensive income (loss), net of tax	(197,532)				(197,532)	(197,532)
Total comprehensive income (loss)						1,485,184
Ending Balance at Dec. 31, 2018		2,500	6,120,436	943,005	(324,373)	6,741,568
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption	42
Cumulative effect of adoption | ASU 2016-01					(3)
Return of capital			(977,500)			(977,500)
Comprehensive income:
Net income (loss)	(989,327)			(989,327)		(989,327)
Other comprehensive income (loss), net of tax	$ 752,985				752,985	752,985
Total comprehensive income (loss)						(236,342)
Ending Balance at Dec. 31, 2019		$ 2,500	$ 5,142,936	$ (46,693)	$ 428,612	$ 5,527,355