Fair Value of Financial Instruments Liabilities Fair Value Measurement on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation liability	$ 1,156	$ 1,006
Interest rate swap asset	5,091	16,428
Interest rate swap liability	10	1,067
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation liability	0	0
Interest rate swap asset	0	0
Interest rate swap liability	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation liability	0	0
Interest rate swap asset	0	0
Interest rate swap liability	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation liability	1,156	1,006
Interest rate swap asset	5,091	16,428
Interest rate swap liability	$ 10	$ 1,067