Retirement Benefit Plans (Schedule of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 20,327	$ 17,858
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,007	6,710
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,320	11,148
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,321	680
Mid Cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,321	680
Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,930	3,553
Large Cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,930	3,553
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,300	2,010
International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,300	2,010
Liability Driven Solution
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,845	2,522
Liability Driven Solution | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,845	2,522
Wells Fargo BlackRock International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	859	727
Wells Fargo BlackRock International Equity | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	859	727
Wells Fargo Core Bond
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,416	1,254
Wells Fargo Core Bond | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,416	1,254
Wells Fargo/Causeway
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	861	741
Wells Fargo/Causeway | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	861	741
Wells Fargo BlackRock Large Cap Growth Index Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,146	1,009
Wells Fargo BlackRock Large Cap Growth Index Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,146	1,009
Wells Fargo BlackRock Large Cap Value Index Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,146	1,006
Wells Fargo BlackRock Large Cap Value Index Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,146	1,006
Wells Fargo Multi-Manager Small Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,387	1,189
Wells Fargo Multi-Manager Small Cap | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,387	1,189
Wells Fargo Russell 2000 Index Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	636	560
Wells Fargo Russell 2000 Index Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	636	560
Wells Fargo S&P Mid Cap Index Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	715	630
Wells Fargo S&P Mid Cap Index Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	715	630
Wells Fargo/MFS Value CIT F
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	578	501
Wells Fargo/MFS Value CIT F | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	578	501
Wells Fargo/T. Rowe Price I Large-Cap Growth Managed CIT
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577	505
Wells Fargo/T. Rowe Price I Large-Cap Growth Managed CIT | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577	505
Wells Fargo/T. Rowe Price Equity Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577	504
Wells Fargo/T. Rowe Price Equity Income | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577	504
Wells Fargo Voya Large Cap Growth CIT F
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577
Wells Fargo Voya Large Cap Growth CIT F | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	577
Cash & Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	456	467
Cash & Short-term Investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 456	$ 467