Unaudited Interim Consolidated Statements of Equity - USD ($)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total Equity
Balance, beginning at Dec. 31, 2014		$ 2,500,000	$ 792,153,000	$ 3,580,641,000	$ 178,691,000	$ 4,553,985,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributed capital	$ 0
Contributed (distributed) capital-parent/child asset transfers			(11,780,000)			(11,780,000)
Comprehensive income (loss):
Net income (loss)	84,230,000			84,230,000		84,230,000
Other comprehensive income (loss), net of tax	51,413,000				51,413,000	51,413,000
Total comprehensive income (loss)						135,643,000
Balance, ending at Mar. 31, 2015		2,500,000	780,373,000	3,664,871,000	230,104,000	4,677,848,000
Balance, beginning at Dec. 31, 2014		2,500,000	792,153,000	3,580,641,000	178,691,000	4,553,985,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributed capital						0
Balance, ending at Dec. 31, 2015		2,500,000	779,973,000	3,663,539,000	64,805,000	4,510,817,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributed capital	5,000,000		5,000,000			5,000,000
Contributed (distributed) capital-parent/child asset transfers			(60,000)			(60,000)
Comprehensive income (loss):
Net income (loss)	(326,131,000)			(326,131,000)		(326,131,000)
Other comprehensive income (loss), net of tax	$ 115,327,000				115,327,000	115,327,000
Total comprehensive income (loss)						(210,804,000)
Balance, ending at Mar. 31, 2016		$ 2,500,000	$ 784,913,000	$ 3,337,408,000	$ 180,132,000	$ 4,304,953,000