Employee Benefit Plans - (Funded Status and Acturial Assumptions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Benefit Plan Disclosure
Unrecognized actuarial gain (loss)		$ (1,104)
Annual Periodic Expense and Actuarial Assumptions
Total net periodic expense			$ 0	$ 0
Pension Plan
Benefit Plan Disclosure
Excess of benefit obligation over plan assets		9,860	13,004
Unrecognized actuarial gain (loss)		(1,517)
Net amount recognized		8,343	13,004
Amounts recognized in the balance sheet consist of:
Accrued benefit liability—current			128
Accrued benefit liability—noncurrent		9,860	12,876
Accumulated other comprehensive		(1,517)
Net amount recognized		8,343	13,004
Summary of plan
Projected benefit obligation		39,206	44,400
Accumulated benefit obligation		39,206	44,400
Fair value of plan assets		29,346	31,395
Annual Periodic Expense and Actuarial Assumptions
Interest cost		1,479
Expected return on plan assets		(2,157)
Settlement (gain)/loss		(1,854)
Total net periodic expense		$ (2,532)
Assumptions used to determine net periodic expense:
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.49%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.00%
Assumptions used to determine benefit obligations:
Discount rate (as a percent)		3.78%
Pension Plan | Forecast
Annual Periodic Expense and Actuarial Assumptions
Total net periodic expense	$ 0
Pension Plan | Maximum
Assumptions used to determine benefit obligations:
Percent of the balance in the project benefit obligation resulting from amortization of accumulated actuarial loss in AOCI at prior year end		10.00%
Postretirement Benefit Plan
Benefit Plan Disclosure
Excess of benefit obligation over plan assets		$ 7,109	18,052
Unrecognized actuarial gain (loss)		413
Net amount recognized		7,522	18,052
Amounts recognized in the balance sheet consist of:
Accrued benefit liability—current		466	628
Accrued benefit liability—noncurrent		6,643	17,424
Accumulated other comprehensive		413
Net amount recognized		7,522	18,052
Summary of plan
Projected benefit obligation		7,109	$ 18,052
Annual Periodic Expense and Actuarial Assumptions
Service cost		74
Interest cost		273
Total net periodic expense		$ 347
Assumptions used to determine net periodic expense:
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.66%
Assumptions used to determine benefit obligations:
Discount rate (as a percent)		3.98%
Assumed health care cost trend rate (as a percent)		5.50%
1% Increase		$ 1,288
1% Decrease		$ (934)
Postretirement Benefit Plan | Forecast
Annual Periodic Expense and Actuarial Assumptions
Total net periodic expense	$ 0
Postretirement Benefit Plan | Maximum
Assumptions used to determine benefit obligations:
Percent of the balance in the project benefit obligation resulting from amortization of accumulated actuarial loss in AOCI at prior year end		10.00%