Employee Benefit Plan (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 685	$ 736	$ 1,458	$ 1,360
Interest cost	676	648	1,344	1,361
Expected return on plan assets	(1,010)	(1,066)	(2,005)	(1,889)
Amortization of net retirement plan actuarial loss	506	526	1,011	941
Amortization of net retirement plan prior service cost (credit)	(31)	(31)	(62)	(62)
Amortization of net retirement plan transition liability	0	0	0	0
Net periodic benefit cost	826	813	1,746	1,711
Life and Health Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	81	51	133	85
Interest cost	87	87	172	181
Expected return on plan assets	0	0	0	0
Amortization of net retirement plan actuarial loss	20	28	48	37
Amortization of net retirement plan prior service cost (credit)	4	4	8	9
Amortization of net retirement plan transition liability	13	17	25	33
Net periodic benefit cost	205	187	386	345
SERP Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	130	100	239	181
Interest cost	184	177	369	358
Expected return on plan assets	0	0	0	0
Amortization of net retirement plan actuarial loss	108	127	230	184
Amortization of net retirement plan prior service cost (credit)	41	45	83	83
Amortization of net retirement plan transition liability	0	0	0	0
Net periodic benefit cost	$ 463	$ 449	$ 921	$ 806