Other Comprehensive Income (Loss) (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense	$ (8,392)		$ (7,698)
Net income	19,802		17,029
Reclassification adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income	116		(182)
Reclassification adjustment | Securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain (loss) on securities transactions	2		(350)
Income tax expense	(1)		143
Net income	1		(207)
Reclassification adjustment | Amortization related to post-retirement obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits, amortization of actuarial losses (gains)	194	[1]	42	[1]
Income tax expense	(79)		(17)
Net income	$ 115		$ 25

[1] This item is included in the computation of net periodic benefit cost. See Note 6. Components of Net Periodic Benefit Cost.