Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014		Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013		Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 603,662	$ 555,951		$ 525,006	$ 508,912	$ 481,656	$ 448,117		$ 363,432	$ 351,070	$ 2,193,531	$ 1,644,275	$ 1,019,061
Insurance costs	476,779	428,184		400,195	381,157	359,992	343,464		269,217	253,912	1,686,315	1,226,585	750,025
Operating income	20,239	21,246		20,029	25,277	23,535	7,287		13,932	21,583	86,791	66,337	61,828
Net income	$ 7,011	$ 725	[1]	$ 6,221	$ 1,540	$ 6,007	$ (7,740)	[2]	$ 4,343	$ 10,537	$ 15,497	$ 13,147	$ 31,832
Basic	$ 0.10	$ 0.01		$ 0.09	$ 0.03	$ 0.11	$ (0.60)		$ 0.09	$ 0.22	$ 0.24	$ 0.26	$ 0.66
Diluted	$ 0.10	$ 0.01		$ 0.09	$ 0.03	$ 0.11	$ (0.60)		$ 0.08	$ 0.20	$ 0.22	$ 0.24	$ 0.63

[1] Included in the results of the third quarter of 2014 is the write-off of debt issuance costs and pre-payment premium as a result of the Company’s amended and restated first lien credit facility. Please read Note 8, “Notes Payable and Borrowings Under Capital Leases,” for additional information

[2] Includes the acquisition of Ambrose Employer Group, LLC during the third and fourth quarter of 2013. Please read Note 4, “Business Combinations,” for additional information.