Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating losses (federal and state)	$ 2,508	$ 2,996
Accrued expenses	9,908	9,381
Accrued workers compensation costs	18,823	13,964
Stock-based compensation	4,643	2,508
Tax benefits relating to uncertain positions	29	20
Tax credits (federal and state)	6,272	9,865
Other	113	354
Total	42,296	39,088
Valuation allowance	(5,276)	(6,945)
Total deferred tax assets	37,020	32,143
Deferred tax liabilities:
Depreciation and amortization	(3,277)	(10,643)
Deferred service revenues	(85,263)	(77,827)
Prepaid health plan expenses	(3,121)	(2,202)
Total deferred tax liabilities	(91,661)	(90,672)
Net non-current deferred tax liabilities	$ (54,641)	$ (58,529)