Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 48,905	$ 41,468	$ 137,752	$ 119,475
Other Comprehensive Income (Loss), net of tax:
Unrealized gain (loss) on securities	3,320	(3,580)	17,861	26,285
Reclassification adjustment for securities gains included in net income	(2,988)	(1)	(4,639)	(666)
Amortization of unrealized loss on derivative financial instruments	0	4	0	12
Amortization of net unrecognized pension and postretirement items	340	379	1,024	877
Other Comprehensive Income (Loss)	672	(3,198)	14,246	26,508
Total Comprehensive Income	$ 49,577	$ 38,270	$ 151,998	$ 145,983