Other Comprehensive Income (Loss) Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense	$ (6,206)		$ (8,007)		$ (13,904)		$ (15,573)
Net income	16,351		19,228		33,380		37,056
Reclassification adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income	(700)		452		(1,394)		957
Reclassification adjustment | Securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain (loss) on securities transactions	110		423		(240)		934
Income tax expense	(45)		(173)		98		(382)
Net income	65		250		(142)		552
Reclassification adjustment | Post-retirement obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits, amortization of actuarial losses (gains)	42	[1]	342	[1]	84	[1]	684	[1]
Income tax expense	(17)		(140)		(34)		(279)
Net income	25		202		50		405
Reclassification adjustment | Post-retirement obligations, unamortized
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits, realized loss related to lump sum pension settlement	(1,336)		0		(1,336)		0
Income tax expense	546		0		546		0
Net income	$ (790)		$ 0		$ (790)		$ 0

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