Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts Receivable.
Contracts receivable, net of allowance for doubtful accounts of $1,654 at March 31, 2017 and $1,030 at December 31, 2016, respectively	$ 303,963	$ 340,871
Retention receivable	64,552	46,394
Contracts receivable and retention	368,515	387,265
Other accounts receivable	1,260	735
Accounts receivable, net	369,775	388,000
Allowance for doubtful accounts	$ 1,654	$ 1,030