Statements of Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Total Equity
Balance at Dec. 31, 2010		$ 2,500	$ 974,921	$ 749,751	$ 181,211	$ 1,908,383
Affiliated asset transfers	0
Distribution to parent	270,000	0	0	(270,000)	0	(270,000)
Cumulative Effect Of Adoption Of New Accounting Principle		0	0	(127,920)	9,660	(118,260)
Comprehensive income:
Net income	156,172	0	0	156,172	0	156,172
Other comprehensive income (loss), net of tax		0	0	0	(23,763)	(23,763)
Balance at Jun. 30, 2011		2,500	974,921	508,003	167,108	1,652,532
Balance at Dec. 31, 2011		2,500	882,670	(25,305)	160,712	1,020,577
Affiliated asset transfers	(10,666)	0	10,666	0	0	10,666
Distribution to parent	248,000	0	0	(248,000)	0	(248,000)
Comprehensive income:
Net income	135,200	0	0	135,200	0	135,200
Other comprehensive income (loss), net of tax		0	0	0	(12,175)	(12,175)
Balance at Jun. 30, 2012		$ 2,500	$ 893,336	$ (138,105)	$ 148,537	$ 906,268