STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (LOSS) (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 34,672	$ 29,929	$ 58,085	$ 64,870
Unrealized gains (losses) on securities:
Change in unrealized holding gains (losses), net	50,910	(136,367)	83,369	(163,415)
Less: Reclassifications adjustment for gains included in net income	(2,569)	(1,519)	(4,039)	(7,412)
Change in unrealized gains (losses) on securities during the period	48,341	(137,886)	79,330	(170,827)
Income tax (expense) benefit	(18,143)	52,087	(29,789)	63,012
Other comprehensive income (loss)	30,198	(85,799)	49,541	(107,815)
Comprehensive income (loss)	$ 64,870	$ (55,870)	$ 107,626	$ (42,945)