Unaudited Interim Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total Equity
Balance, beginning at Dec. 31, 2013		$ 2,500	$ 804,237	$ 3,542,838	$ 56,646	$ 4,406,221
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend to parent				(338,000)		(338,000)
Contributed (distributed) capital-parent/children asset transfers			130			130
Comprehensive income (loss):
Net income (loss)	$ 528,239			528,239		528,239
Other comprehensive income (loss), net of tax	106,749				106,749	106,749
Total comprehensive income (loss)						634,988
Balance, ending at Jun. 30, 2014		2,500	804,367	3,733,077	163,395	4,703,339
Balance, beginning at Dec. 31, 2014		2,500	792,153	3,580,641	178,691	4,553,985
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend to parent				(230,000)		(230,000)
Contributed (distributed) capital-parent/children asset transfers			(12,180)			(12,180)
Comprehensive income (loss):
Net income (loss)	298,659			298,659		298,659
Other comprehensive income (loss), net of tax	$ (83,591)				(83,591)	(83,591)
Total comprehensive income (loss)						215,068
Balance, ending at Jun. 30, 2015		$ 2,500	$ 779,973	$ 3,649,300	$ 95,100	$ 4,526,873