Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$ 277,977	$ 237,866	$ 237,952
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	103,044	(115,245)	33,412
Change in net unrealized gain on securities transferred to held-to-maturity	(35,441)	(35,682)	(657)
Reclassification adjustment for net (gains) losses included in net income	(38)	(1,176)	(4,314)
Total securities available for sale and transferred securities	67,565	(152,103)	28,441
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	(34,837)	35,293	(9,405)
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	0	(49)	(783)
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	(30,604)	(37,380)	(37,380)
Interest rate swap on junior subordinated deferrable interest debentures	0	4,064	4,224
Total derivatives	(30,604)	(33,365)	(33,939)
Other comprehensive income (loss), before tax	2,124	(150,175)	(14,903)
Deferred tax expense (benefit) related to other comprehensive income	744	(52,561)	(5,217)
Other comprehensive income (loss), net of tax	1,380	(97,614)	(9,686)
Comprehensive income	$ 279,357	$ 140,252	$ 228,266