Basis of Presentation and Nature of Operations - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2017 Office
Reclassification of Deferred Compensation Liabilities from Accrued Salaries and Benefits to Long-term Noncurrent Classification
Basis of Presentation and Nature of Operations [Line Items]
Prior period reclassification adjustment | $	$ 4.3
Domestic
Basis of Presentation and Nature of Operations [Line Items]
Number of offices		59
International
Basis of Presentation and Nature of Operations [Line Items]
Number of offices		23