Employee Benefits (Obligations and Funded Status of the Plan) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Retirement Plans
Change in plan assets:
Fair value of plan assets at end of year	$ 220,568	$ 191,369
Retirement Income Plan
Change in projected benefit obligation:
Benefit obligation at end of prior year	296,293	242,718
Service cost	8,530	6,590	5,888
Interest cost	12,594	12,871	12,507
Amendments	0	0	0
Actuarial loss	12,417	42,508
Benefits paid	(8,988)	(8,394)
Benefit obligation at end of year	320,846	296,293	242,718
Change in plan assets:
Fair value of plan assets at end of prior year	191,369	171,341
Actual return on plan assets	20,187	16,422
Employer contribution	18,000	12,000
Benefits paid	(8,988)	(8,394)
Fair value of plan assets at end of year	220,568	191,369	171,341
Funded status at end of year	(100,278)	(104,924)
Non-Qualified Retirement Plans
Change in projected benefit obligation:
Benefit obligation at end of prior year	26,547	24,008
Service cost	299	260	176
Interest cost	963	1,116	1,122
Amendments	0	0	838
Actuarial loss	1,338	2,980
Benefits paid	(1,906)	(1,817)
Benefit obligation at end of year	27,241	26,547	24,008
Change in plan assets:
Fair value of plan assets at end of prior year	0	0
Actual return on plan assets	0	0
Employer contribution	1,906	1,817
Benefits paid	(1,906)	(1,817)
Fair value of plan assets at end of year	0	0	0
Funded status at end of year	$ (27,241)	$ (26,547)