Pension Plans and Other Postretirement Benefits - Fair Value of Plan Assets (Details) - Defined Benefit Plan - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total	$ 22,090	$ 25,843	$ 25,446
Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total	11,003	12,165
Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total	800	588
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total	800	588
Level 1 | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
Level 1 | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total	800	588
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total	21,290	25,255
Level 2 | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total	11,003	12,165
Level 2 | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
Level 3 | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
Level 3 | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
United States | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	8,198	10,517
United States | Level 1 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
United States | Level 2 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	8,198	10,517
United States | Level 3 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
International | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	2,089	2,573
International | Level 1 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
International | Level 2 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	2,089	2,573
International | Level 3 | Equity security funds
Defined Benefit Plan Disclosure [Line Items]
Total	$ 0	$ 0