Pension and Other Post Retirement Benefit Plans - Schedule of Plan Assets by Level (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 85,213	$ 83,557	$ 71,396
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	78,280	64,064
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,123	3,778
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	14,598	10,646
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	2,545	2,278
Quoted Prices in Active Markets for Identical Assets (Level 1) | Taxable Bond
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	12,198	7,974
Quoted Prices in Active Markets for Identical Assets (Level 1) | Large Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	22,137	19,611
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mid Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	10,676	10,304
Quoted Prices in Active Markets for Identical Assets (Level 1) | Small Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,264	4,680
Quoted Prices in Active Markets for Identical Assets (Level 1) | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,030	3,093
Quoted Prices in Active Markets for Identical Assets (Level 1) | Specialty Alternative Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,709	1,700
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	6,933	19,493
Significant Other Observable Inputs (Level 2) | Government Agency and Municipal Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,679	6,855
Significant Other Observable Inputs (Level 2) | Certificates of Deposit
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,254	1,268
Significant Other Observable Inputs (Level 2) | Common Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets		4,744
Significant Other Observable Inputs (Level 2) | Common Equity Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets		6,626
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets
Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	85,213	83,557
Fair Value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,123	3,778
Fair Value | Corporate Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	14,598	10,646
Fair Value | Government Agency and Municipal Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,679	6,855
Fair Value | Certificates of Deposit
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,254	1,268
Fair Value | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	2,545	2,278
Fair Value | Common Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets		4,744
Fair Value | Common Equity Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets		6,626
Fair Value | Taxable Bond
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	12,198	7,974
Fair Value | Large Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	22,137	19,611
Fair Value | Mid Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	10,676	10,304
Fair Value | Small Cap Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	5,264	4,680
Fair Value | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,030	3,093
Fair Value | Specialty Alternative Equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 1,709	$ 1,700