Fair Value Measurements (Assets and Liabilities Measured on Recurring Basis) (Details) - Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 31,979	$ 31,201
Deferred compensation plan obligations	20,838	19,864
Total	20,894	19,973
Grantor Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	20,838	19,864
Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	7,312	7,446
Interest Rate Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3,829	3,891
Derivative liabilities	56	109
Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	28,150	27,310
Deferred compensation plan obligations	20,838	19,864
Total	20,838	19,864
Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	20,838	19,864
Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	7,312	7,446
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	3,829	3,891
Total	56	109
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3,829	3,891
Derivative liabilities	56	109
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0	0
Total	$ 0	$ 0