Retirement Benefit Plans (Summary of Fair Value of Plan Assets by Level) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 192,734	$ 161,369
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,227	28,624
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	159,714	131,811
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	793	934	$ 1,077
Exchange traded funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,526	28,329
Exchange traded funds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,526	28,329
Exchange traded funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Exchange traded funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	701	295
Cash and cash equivalents [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	701	295
Cash and cash equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96,429	80,783
Fixed Income Funds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed Income Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96,429	80,783
Fixed Income Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63,285	51,028
Equity Funds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63,285	51,028
Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Insurance Company Investment Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	793	934
Insurance Company Investment Contract [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Insurance Company Investment Contract [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Insurance Company Investment Contract [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 793	$ 934