Employee Benefit Plans - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Pension
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	$ (22,065)	$ (27,710)
Deferred income tax benefit	1,927	1,927
AOCI	(20,138)	(25,783)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	(67)	45
Deferred income tax benefit	6	6
AOCI	$ (61)	$ 51