Employee Benefits (Schedule of Net Funded Status) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Qualified Pension Plan [Member]
Change in Benefit Obligation:
Benefit obligation at beginning of period	$ 57,257	$ 46,556
Service cost	2,574	2,314	2,337
Interest cost	2,823	2,578	2,507
Actuarial loss	9,535	7,298
Benefits paid	(1,440)	(1,371)
Administrative expenses	(134)	(118)
Benefit obligation at end of period	70,615	57,257	46,556
Change in Plan Assets:
Fair value of plan assets at beginning of period	38,330	36,070
Actual return on plan assets	4,322	749
Employer contribution	10,000	3,000
Benefits paid	(1,440)	(1,371)
Administrative expenses	(134)	(118)
Fair value of plan assets at end of period	51,078	38,330	36,070
Unfunded status at end of period	(19,537)	(18,927)
Non-Qualified Retirement Plans [Member]
Change in Benefit Obligation:
Benefit obligation at beginning of period	11,321	9,953
Service cost	150	71	93
Interest cost	503	495	515
Actuarial loss	1,315	1,534
Benefits paid	(720)	(732)
Administrative expenses	0	0
Benefit obligation at end of period	12,569	11,321	9,953
Change in Plan Assets:
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Employer contribution	720	732
Benefits paid	(720)	(732)
Administrative expenses	0	0
Fair value of plan assets at end of period	0	0	0
Unfunded status at end of period	$ (12,569)	$ (11,321)