Fair Value Measurement - Assets and Liabilities on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 60,535	$ 1,128
Restricted cash and restricted investments	16,575
Total	77,110
Level 1
Assets
Cash and cash equivalents	60,535	1,128
Restricted cash and restricted investments	16,575
Total	77,110
Liabilities
Contingent consideration	0	0
Level 2
Assets
Cash and cash equivalents	0	0
Restricted cash and restricted investments	0
Total	0
Liabilities
Contingent consideration	0	0
Level 3
Assets
Cash and cash equivalents	0	0
Restricted cash and restricted investments	0
Total	0
Liabilities
Contingent consideration	$ 8,700	$ 8,300