Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 304,261	$ 279,328	$ 277,977
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	(175,061)	(12,450)	103,044
Change in net unrealized gain on securities transferred to held-to-maturity	(32,207)	(33,601)	(35,441)
Reclassification adjustment for net (gains) losses included in net income	(14,975)	(69)	(38)
Total securities available for sale and transferred securities	(222,243)	(46,120)	67,565
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	1,914	(3,877)	(37,524)
Reclassification adjustment for net amortization of actuarial gain(loss) and for SERP settlement costs included in net income, before tax amount	7,274
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit)		6,995	2,687
Total defined-benefit post-retirement benefit plans	9,188	3,118	(34,837)
Reclassification adjustments for (gains) losses included in net income:
Reclassification adjustment for gains on interest rate swaps on variable-rate loans included in net income	0	0	(30,604)
Total derivatives	0	0	(30,604)
Other comprehensive income (loss), before tax	(213,055)	(43,002)	2,124
Deferred tax expense (benefit)	(74,569)	(15,051)	744
Other comprehensive income (loss), net of tax	(138,486)	(27,951)	1,380
Comprehensive income	$ 165,775	$ 251,377	$ 279,357