Other Comprehensive Income (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense	$ (8,736)	$ (8,392)
Net income	20,973	19,802
Unrealized gains on securities available for sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits, amortization of actuarial losses (gains)	96	2
Income tax expense	39	1
Net of tax	57	1
Reclassification adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax	198	116
Reclassification adjustment [Member] | Unrealized gains on securities available for sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain on securities transactions	96	2
Income tax expense	(39)	(1)
Net income	57	1
Reclassification adjustment [Member] | Post-retirement obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits, amortization of actuarial losses (gains)	236	194
Income tax expense	95	79
Net of tax	$ 141	$ 115