Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2015 $ / shares	Jun. 30, 2015 $ / shares shares	Jun. 30, 2014 $ / shares shares	Jun. 30, 2015 USD ($) Office $ / shares shares	Jun. 30, 2014 $ / shares shares
Accounting Policies [Abstract]
Number of domestic field offices of parent company				62
Number of subsidiaries with international offices				1
Common stock excluded from the computation of dilutive earnings per share | shares		0	0	0	0
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 | $				$ 300
Health insurance maximum aggregate amount of risk of loss liability for employee insurance plans | $				$ 450
Dividend (in dollars per share) | $ / shares	$ 0.11	$ 0.11	$ 0.10	$ 0.22	$ 0.20