Changes in Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Postretirement Benefit Plan
Change in Projected Benefit Obligation [Abstract]
Accumulated postretirement benefit obligation at beginning of year	$ 2,427	$ 2,552
Service cost	71	83	$ 56
Interest cost	65	79	76
Benefit payments	(240)	(202)
Actuarial gain	759	85
Accumulated postretirement benefit obligation at end of year	1,564	2,427	2,552
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Funded status – net prepaid (liability)	(1,564)	(2,427)
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	(234)	(246)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	(1,330)	(2,181)
Net amount recognized	(1,564)	(2,427)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	2,574	2,024
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	2,574	2,024
Pension Plans, Defined Benefit
Change in Projected Benefit Obligation [Abstract]
Accumulated postretirement benefit obligation at beginning of year	162,290
Projected benefit obligation at beginning of year	162,941	193,322
Service cost	377	549	453
Interest cost	5,182	6,938	6,885
Settlement Gain	0	(2,162)
Curtailment Loss	0	2,154
Benefit payments	(9,459)	(25,383)
Actuarial gain	(4,361)	(12,477)
Projected benefit obligation at end of year	154,680	162,941	193,322
Accumulated postretirement benefit obligation at end of year	154,044	162,290
Change in Plan Assets [Abstract]
Fair value of plan assets at beginning of year	154,506	183,671
Defined Benefit Plan, Actual (Loss) Return on Plan Assets	12,253	(4,140)
Employer contributions	414	358
Fair value of plan assets at end of year	157,714	154,506	$ 183,671
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Funded status – net prepaid (liability)	3,034	(8,435)
Defined Benefit Plan, Assets for Plan Benefits	8,501	8,422
Accrued liabilities	(367)	(362)
Pension benefit obligations	(5,100)	(16,495)
Net amount recognized	3,034	(8,435)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(25,665)	(35,972)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost, before Tax	(517)	(717)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	$ 26,182	$ (36,689)