Pension and Other Postretirement Benefits - Fair Value Hierarchy - Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	$ 98,456	$ 86,591
Fair Value of Plan Assets measured at NAV	52,130	49,450
Fair Value of Plan Assets		136,041
Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,983	1,711
Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	11,953	10,061
Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	84,520	74,819
Real Estate Fund [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets		2,041
Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	1,957	1,581
Fair Value of Plan Assets		49,197
Domestic [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	1,957	1,581
Domestic [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	449	302
Domestic [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	449	302
Domestic [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Equity Securities Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	1,508	1,279
Domestic [Member] | Equity Securities Small Cap [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	1,508	1,279
Domestic [Member] | Equity Securities Small Cap [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Equity Securities Small Cap [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Domestic [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets measured at NAV	1,480	1,431
Domestic [Member] | Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets measured at NAV	48,527	46,185
Foreign [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	96,499	85,010
Fair Value of Plan Assets		86,844
Foreign [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	26	130
Foreign [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	11,953	10,061
Foreign [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	84,520	74,819
Foreign [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	26	130
Foreign [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	26	130
Foreign [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Cash and Cash Equivalents [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	2,951	2,753
Foreign [Member] | Fixed Income Funds [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Fixed Income Funds [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	2,951	2,753
Foreign [Member] | Fixed Income Funds [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Insurance Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	82,092	72,778
Foreign [Member] | Insurance Contract [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Insurance Contract [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Insurance Contract [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	82,092	72,778
Fair Value of Plan Assets		72,778
Foreign [Member] | Equity Funds Diversified [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	9,002	7,308
Foreign [Member] | Equity Funds Diversified [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Equity Funds Diversified [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	9,002	7,308
Foreign [Member] | Equity Funds Diversified [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	2,428	2,041
Foreign [Member] | Real Estate Fund [Member] | Fair Value Inputs Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Real Estate Fund [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	0	0
Foreign [Member] | Real Estate Fund [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets excluding assets measured at NAV	2,428	2,041
Foreign [Member] | Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets measured at NAV	$ 2,123	$ 1,834