Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Amounts owed to employees participating in the Deferred Compensation Plan	$ 3,600	$ 3,900
Obligations
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	3,000
New level 3 liability	0
Total gains (losses) reported in earnings	0
Transfers into or out of Level 3	0
Balance at end of period	$ 3,000