Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 208,393	$ 171,753	$ 161,625
Unrealized (losses) gains on available for sale investment securities:
Unrealized (loss) gain on securities	(24,326)	10,432	(14,891)
Reclassification adjustment for securities gains included in net income	(30)	(5,894)	(1,657)
Non-credit related unrealized gain (loss) on other-than-temporarily impaired debt securities	222	185	(185)
Net unrealized (losses) gains on available for sale investment securities	(22,036)	4,723	(16,733)
Unrealized gains on derivative financial instruments:
Amortization of unrealized loss on derivative financial instruments	0	0	16
Reclassification adjustment for loss on derivative financial instruments included in net income	2,098	0	0
Defined benefit pension plan and postretirement benefits:
Unrecognized pension and postretirement income (cost)	1,400	(609)	(931)
Amortization of net unrecognized pension and postretirement income	1,648	1,361	1,216
Net unrealized gains on defined benefit pension and postretirement plans	3,048	752	285
Other Comprehensive (Loss) Income	(18,988)	5,475	(16,432)
Total Comprehensive Income	$ 189,405	$ 177,228	$ 145,193