Employee Benefit Plans - Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension
Defined Benefit Plan Disclosure [Line Items]
Net gains (losses)	$ 3,119	$ (477)	$ (37,559)
Amortization of losses (gains)	2,526	3,733	6,542
Amortization of prior service cost	0	13	576
Amortization of negative plan amendment	0	0	0
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net gains (losses)	(99)	123	(2,250)
Amortization of losses (gains)	(13)	12	288
Amortization of prior service cost	0	0	8
Amortization of negative plan amendment	$ 0	$ 0	$ (137)