Pension and Other Retirement Plans - Amounts Included in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses, net of tax	$ (66,397)	$ (59,705)
Unrecognized prior service (cost) credit, net of tax	1,514	2,314
Total	(64,883)	(57,391)
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses, net of tax	(66,212)	(59,217)
Unrecognized prior service (cost) credit, net of tax	(568)	0
Total	(66,780)	(59,217)
Other Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized net actuarial losses, net of tax	(185)	(488)
Unrecognized prior service (cost) credit, net of tax	2,082	2,314
Total	$ 1,897	$ 1,826