Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts Receivable.
Contracts receivable, net of allowance for doubtful accounts of $1,654 at June 30, 2017 and $1,030 at December 31, 2016, respectively	$ 294,670	$ 340,871
Retention receivable	56,251	46,394
Contracts receivable and retention	350,921	387,265
Other accounts receivable	4,310	735
Accounts receivable, net	355,231	388,000
Allowance for doubtful accounts	$ 1,654	$ 1,030