Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 131,961	$ 143,627	$ 132,511
Other comprehensive income (loss), net of tax:
Net (losses) gains arising during the period	(13,239)	5,682	1,513
Less reclassification adjustment for net gains included in net income	(8,522)	(1,545)	(19,674)
Total	(21,761)	4,137	(18,161)
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	3,637	9,942	(26,656)
Less reclassification adjustment for credit impairment losses included in net income	(268)	2,449	11,633
Defined benefit pension plan, total	3,369	12,391	(15,023)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	2,400	(3,351)	(14,157)
Less reclassification adjustment for net losses included in net income	4,005	3,760	1,780
Total	6,405	409	(12,377)
Defined benefit pension plan
Net gains (losses) arising during the period	21,577	(6,839)	(12,404)
Amortization of prior service cost	1,454	38	348
Amortization of net loss	1,145	1,396	895
Recognition of loss due curtailment	468
Total	24,644	(5,405)	(11,161)
Total other comprehensive income (loss)	12,657	11,532	(56,722)
Total comprehensive income	$ 144,618	$ 155,159	$ 75,789