Pension and Other Post-Retirement Benefit Plans (Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Hedge funds and private equity [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 25,831	$ 28,649
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	715,885	672,153	$ 719,787
Defined Benefit Plan Assets fair value hierarchy	656,611	613,787
Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	80,965	66,777
Pension Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	575,646	547,010
Pension Plans [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	59,273	58,366
Pension Plans [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	715,884	672,153
Pension Plans [Member] | Common trust funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Common trust funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3,469	4,354
Pension Plans [Member] | Common trust funds [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3,469	4,354
Pension Plans [Member] | Corporate stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	20,818	14,832
Pension Plans [Member] | Corporate stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Corporate stock [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	20,818	14,832
Pension Plans [Member] | Mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	59,370	46,991
Pension Plans [Member] | Mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	114,940	99,056
Pension Plans [Member] | Mutual funds [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	174,310	146,047
Pension Plans [Member] | Fixed income investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	777	4,954
Pension Plans [Member] | Fixed income investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	457,237	443,600
Pension Plans [Member] | Fixed income investments [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 458,014	$ 448,554