Pension Plan Pension plan net periodic benefit costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	$ 11,759	$ 14,347	$ 14,075
Interest cost on projected benefit obligation	28,835	25,596	26,312
Expected return on plan assets	(41,047)	(41,347)	(37,878)
Amortization of prior service cost (credit)	98	98	98
Recognized net loss	4,106	9,291	7,844
Additional amount recognized due to curtailment/settlement	0	0	0
Net pension benefit cost	3,751	7,985	10,451
Change in prior service cost	0	0	0
Change in net gain or loss	66,165	(51,465)	20,365
Amortization of prior service cost (credit)	(98)	(98)	(98)
Amortization of net gain (loss)	(4,106)	(9,291)	(7,844)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	61,961	(60,854)	12,423
Amount Recognized in Net Periodic Benefit Cost and Other Comprehensive Income (Loss), before Tax	65,712	(52,869)	22,874
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	256	340	380
Interest cost on projected benefit obligation	342	311	408
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	0	0	0
Recognized net loss	91	261	169
Additional amount recognized due to curtailment/settlement	0	276	198
Net pension benefit cost	689	1,188	1,155
Change in prior service cost	0	0	0
Change in net gain or loss	660	(1,052)	815
Amortization of prior service cost (credit)	0	0	0
Amortization of net gain (loss)	(91)	(261)	(169)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	569	(1,313)	646
Amount Recognized in Net Periodic Benefit Cost and Other Comprehensive Income (Loss), before Tax	$ 1,258	$ (125)	$ 1,801