Summary of Significant Accounting Policies - Restricted Cash and Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Restricted cash
Restricted cash	$ 931	$ 958
Accounts Receivable [Abstract]
Allowance for doubtful accounts receivable	3,000	2,600
Retainage	40,109	$ 42,547
Retainage, long-term	$ 6,000