Fair Value Measurement Financial Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments under executive deferred compensation plan	$ 25,494,000	$ 22,037,000
Private equity securities	38,000	35,000
Private equity securities measured at net asset value	5,121,000	5,498,000
Obligations under executive deferred compensation plan	25,494,000	22,037,000
Foreign currency forward contracts, liabilities	4,954,000	182,000
Transfers between levels 1 and 2	0
Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	659,874,000	606,957,000
Other Postretirement Benefits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	834,000	2,232,000	$ 3,292,000
Quoted Prices in Active Markets for Identical Items (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments under executive deferred compensation plan	25,494,000	22,037,000
Private equity securities	38,000	35,000
Private equity securities measured at net asset value	0	0
Obligations under executive deferred compensation plan	25,494,000	22,037,000
Foreign currency forward contracts, liabilities	0	0
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	493,848,000	460,247,000
Quoted Prices in Active Markets for Identical Items (Level 1) | Other Postretirement Benefits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Similar Items (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments under executive deferred compensation plan	0	0
Private equity securities	0	0
Private equity securities measured at net asset value	0	0
Obligations under executive deferred compensation plan	0	0
Foreign currency forward contracts, liabilities	4,954,000	182,000
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	69,612,000	60,598,000
Quoted Prices in Active Markets for Similar Items (Level 2) | Other Postretirement Benefits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	834,000	2,232,000
Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments under executive deferred compensation plan	0	0
Private equity securities	0	0
Private equity securities measured at net asset value	0	0
Obligations under executive deferred compensation plan	0	0
Foreign currency forward contracts, liabilities	0	0
Unobservable Inputs (Level 3) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Other Postretirement Benefits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Measured at Fair Value | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	563,460,000	520,845,000
Measured at Fair Value | Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	493,848,000	460,247,000
Measured at Fair Value | Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	69,612,000	60,598,000
Measured at Fair Value | Unobservable Inputs (Level 3) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Absolute Return Measured At Net Asset Value | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	96,414,000	86,112,000
Absolute Return Measured At Net Asset Value | Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Absolute Return Measured At Net Asset Value | Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	0	0
Absolute Return Measured At Net Asset Value | Unobservable Inputs (Level 3) | Pension Plans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	$ 0	$ 0