Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 49,480	$ 43,380
Other Comprehensive (Loss) Income, net of tax:
Unrealized (loss) gain on securities	(27,644)	4,273
Reclassification adjustment for securities gains included in net income	(16)	(719)
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	(224)	0
Amortization of net unrecognized pension and postretirement items	339	343
Other Comprehensive (Loss) Income	(27,097)	3,897
Total Comprehensive Income	$ 22,383	$ 47,277