Fair Value Measurement - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Level 1
Fair Value Assets Liabilities Measured On Recurring Basis [Line Items]
Deferred Compensation Liability	$ 0	$ 0
Level 2
Fair Value Assets Liabilities Measured On Recurring Basis [Line Items]
Deferred Compensation Liability	(12,927)	(11,978)
Level 3
Fair Value Assets Liabilities Measured On Recurring Basis [Line Items]
Deferred Compensation Liability	$ 0	$ 0