Consolidated Statements of Comprehensive Income (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 Comprehensive Income [Abstract]
Net income (loss)	$ 120,867	$ 33,483	$ 149,654	$ 83,533
Unrealized gains (losses) on investments available-for-sale:
Unrealized holding gains (losses) arising during the period	23,520	(65,763)	51,908	(74,853)
Less: Reclassification adjustments for gains included in earnings	(1,928)	(5,647)	(2,236)	(22,936)
Unrealized gains (losses) on investments available-for-sale, net	21,592	(71,410)	49,672	(97,789)
Defined benefit pension plans:
Prior service cost arising during the period	0	0	0	0
Net loss arising during the period	0	0	0	0
Less: Amortization of prior service cost and net loss included in net periodic pension cost	150	643	300	1,286
Defined benefit pension plans, net	150	643	300	1,286
Other comprehensive income (loss) before tax	21,742	(70,767)	49,972	(96,503)
Income tax expense (benefit) related to components of other comprehensive income	7,683	(24,882)	17,556	(33,910)
Other comprehensive income (loss), net of tax	14,059	(45,885)	32,416	(62,593)
Comprehensive income (loss)	$ 134,926	$ (12,402)	$ 182,070	$ 20,940