Employee Benefits (Obligations and Funded Status of the Plan) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retirement Plans
Change in plan assets:
Fair value of plan assets at end of year	$ 191,369	$ 171,341
Retirement Income Plan
Change in projected benefit obligation:
Benefit obligation at end of prior year	242,718	215,944
Service cost	6,590	5,888	5,414
Interest cost	12,871	12,507	11,942
Amendments	0	0	0
Actuarial loss	42,508	16,008
Benefits paid	(8,394)	(7,629)
Benefit obligation at end of year	296,293	242,718	215,944
Change in plan assets:
Fair value of plan assets at end of prior year	171,341	155,140
Actual return on plan assets	16,422	17,030
Employer contribution	12,000	6,800
Benefits paid	(8,394)	(7,629)
Fair value of plan assets at end of year	191,369	171,341	155,140
Funded status at end of year	(104,924)	(71,377)
Non-Qualified Retirement Plans
Change in projected benefit obligation:
Benefit obligation at end of prior year	24,008	21,767
Service cost	260	176	120
Interest cost	1,116	1,122	1,241
Amendments	0	838	0
Actuarial loss	2,980	1,822
Benefits paid	(1,817)	(1,717)
Benefit obligation at end of year	26,547	24,008	21,767
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	1,817	1,717
Benefits paid	(1,817)	(1,717)
Fair value of plan assets at end of year	0	0	0
Funded status at end of year	$ (26,547)	$ (24,008)