Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 161,625	$ 149,502	$ 157,894
Unrealized (losses) gains on available for sale investment securities:
Unrealized (loss) gain on securities	(14,891)	(7,717)	33,734
Reclassification adjustment for securities gains included in net income	(1,657)	(5,892)	(1,327)
Non-credit related unrealized (loss) gain on other-than-temporarily impaired debt securities	(185)	239	780
Net unrealized (losses) gains on available for sale investment securities	(16,733)	(13,370)	33,187
Unrealized gains on derivative financial instruments:
Amortization of unrealized loss on derivative financial instruments	16	75	136
Reclassification adjustment for loss on derivative financial instruments included in net income	0	2,456	0
Net unrealized gains on derivative financial instruments	16	2,531	136
Defined benefit pension plan and postretirement benefits:
Unrecognized pension and postretirement (cost) income	(931)	4,680	(13,168)
Amortization of net unrecognized pension and postretirement income	1,216	1,864	408
Non-credit related unrealized (loss) gain on other-than-temporarily impaired debt securities	0	0	(944)
Net unrealized gains (losses) on pension and postretirement plans	285	6,544	(13,704)
Other Comprehensive (Loss) Income	(16,432)	(4,295)	19,619
Total Comprehensive Income	$ 145,193	$ 145,207	$ 177,513