Employee Benefits (Components of Net Periodic Benefit Cost) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (on a pre-tax basis):
Recognized in other comprehensive income	$ 13,493	[1]	$ (20,406)	[1]	$ 8,445	[1]
Qualified Pension Plan [Member]
Net Periodic Benefit Cost:
Service cost	2,152		2,720		2,574
Interest cost	2,891		2,883		2,823
Expected return on plan assets	(4,063)		(3,725)		(2,985)
Amortization of prior service (credit) cost	(23)		(30)		(33)
Recognized net actuarial loss	461		1,321		982
Curtailments	0		(61)		0
Net periodic benefit cost	1,418		3,108		3,361
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (on a pre-tax basis):
Net loss (gain)	10,993		(14,572)		7,216
Prior service cost (credit)	23		30		33
Curtailment	0		(4,000)		0
Recognized in other comprehensive income	11,016		(18,542)		7,249
Total recognized in net periodic benefit cost and other comprehensive income (loss)	12,434		(15,434)		10,610
Non-Qualified Retirement Plans [Member]
Net Periodic Benefit Cost:
Service cost	46		181		150
Interest cost	478		462		503
Expected return on plan assets	0		0		0
Amortization of prior service (credit) cost	(1)		(1)		(1)
Recognized net actuarial loss	70		175		119
Curtailments	0		(1)		0
Net periodic benefit cost	593		816		771
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (on a pre-tax basis):
Net loss (gain)	2,476		(1,506)		1,195
Prior service cost (credit)	1		1		1
Curtailment	0		(359)		0
Recognized in other comprehensive income	2,477		(1,864)		1,196
Total recognized in net periodic benefit cost and other comprehensive income (loss)	$ 3,070		$ (1,048)		$ 1,967

[1] Included in salaries and employee benefits expense in the Consolidated Statements of Income.