Employee Benefit Plans - Amounts Recognized in the Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amounts Recognized in the Balance Sheet
Long-term liabilities	$ 35,293	$ 35,827
Postretirement Benefits Other than Pensions
Amounts Recognized in the Balance Sheet
Current liabilities	1,333	1,249	$ 1,441
Long-term liabilities	35,293	35,827	33,554
Amounts recognized in the balance sheet	$ 36,626	$ 37,076	$ 34,995