Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Trade accounts payable	$ 24,189	$ 14,534
Accrued salaries, vacation and benefits	22,205	18,049
Other accrued expenses	26,256	23,379
Accrued contingent consideration	2,724	3,590
Negative cash book balance	2,906	5,044
Accounts Payable and Accrued Liabilities, Current, Total	$ 78,280	$ 64,596