Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 149,502	$ 157,894	$ 161,840
Unrealized (losses) gains on available for sale investment securities:
Unrealized (loss) gain on securities	(7,717)	33,734	(49,607)
Reclassification adjustment for securities gains included in net income	(5,892)	(1,327)	(5,203)
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	239	780	1,977
Net unrealized (losses) gains on available for sale investment securities	(13,370)	33,187	(52,833)
Unrealized gains on derivative financial instruments:
Unrealized gain on derivative financial instruments	75	136	136
Reclassification adjustment for loss on derivative financial instruments included in net income	2,456	0	0
Net unrealized gains on derivative financial instruments	2,531	136	136
Defined benefit pension plan and postretirement benefits:
Unrecognized pension and postretirement income (cost)	4,680	(13,168)	8,369
Amortization of net unrecognized pension and postretirement income	1,864	408	1,312
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	0	(944)	0
Net unrealized gains (losses) on pension and postretirement plans	6,544	(13,704)	9,681
Other Comprehensive (Loss) Income	(4,295)	19,619	(43,016)
Total Comprehensive Income	$ 145,207	$ 177,513	$ 118,824