Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 $ / shares shares	Jun. 30, 2015 $ / shares shares	Jun. 30, 2016 USD ($) Office subsidiary $ / shares shares	Jun. 30, 2015 $ / shares shares
Accounting Policies [Abstract]
Number of domestic field offices of parent company | Office			62
Number of subsidiaries with international offices | subsidiary			1
Percentage of net service revenue from international operations (less than)	2.00%	2.00%	2.00%	2.00%
Health insurance maximum risk of loss liability per employee insurance plan (up to)			$ 350,000
Health insurance maximum aggregate amount of risk of loss liability for employee insurance plans (up to)			$ 450,000
Dividend (in dollars per share) | $ / shares	$ 0.12	$ 0.11	$ 0.24	$ 0.22
Common stock equivalents (in shares) | shares	155	203	151	203