Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts Receivable.
Contracts receivable, net of allowance for doubtful accounts of $1,030 at December 31, 2016 and $480 at December 31, 2015, respectively	$ 340,871	$ 288,300
Retention receivable	46,394	31,396
Contracts receivable and retention	387,265	319,696
Other accounts receivable	735	892
Accounts receivable, net	388,000	320,588
Allowance for doubtful accounts	$ 1,030	$ 480