Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 45,467	$ 39,750	$ 88,847	$ 78,007
Other Comprehensive Income, net of tax:
Unrealized gain on securities	10,268	12,839	14,541	29,865
Reclassification adjustment for securities gains included in net income	(932)	(49)	(1,651)	(665)
Amortization of unrealized loss on derivative financial instruments	0	4	0	8
Amortization of net unrecognized pension and postretirement items	341	32	684	498
Other Comprehensive Income	9,677	12,826	13,574	29,706
Total Comprehensive Income	$ 55,144	$ 52,576	$ 102,421	$ 107,713