Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 60,253	$ (8,939)	$ 148,609	$ 140,715
Unrealized gains (losses) on investments available-for-sale:
Unrealized holding gains (losses) arising during the period	11,406	2,103	(3,498)	54,011
Less: Reclassification adjustments for gains included in earnings	82	(346)	(2,087)	(2,582)
Unrealized gains (losses) on investments available-for-sale, net	11,488	1,757	(5,585)	51,429
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	640	150	1,920	450
Defined benefit pension plans, net	640	150	1,920	450
Other comprehensive income (loss) before tax	12,128	1,907	(3,665)	51,879
Income tax expense (benefit) related to components of other comprehensive income	4,277	680	(1,238)	18,236
Other comprehensive income (loss), net of tax	7,851	1,227	(2,427)	33,643
Comprehensive income (loss)	$ 68,104	$ (7,712)	$ 146,182	$ 174,358