Employee Benefit Plans Fair Values of Plan Investments by Hierarchy 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	$ 18,499	$ 16,631	$ 15,717
U.S. Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,131	1,826
Common trust funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		5,207
Equity securities [Member] | Information technology [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		976
Equity securities [Member] | Financial [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		813
Equity securities [Member] | Industrials [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,212
Equity securities [Member] | Healthcare [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,393
Equity securities [Member] | Consumer [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,131
Equity securities [Member] | Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,275
Mutual and exchange traded funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,368	1,798
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,368	14,805
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common trust funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		5,207
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Information technology [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		976
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Financial [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		813
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Industrials [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,212
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Healthcare [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,393
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Consumer [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,131
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member] | Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,275
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mutual and exchange traded funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,368	1,798
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,131	1,826
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 7,131	$ 1,826