Percentage-of-completion method (Details 7) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Costs and estimated earnings in excess of billings on uncompleted contracts		$ 109,541	$ 64,558
Billings in excess of costs and estimated earnings on uncompleted contracts		84,123	64,832
Short-term retainage	[1]	57,134	45,109
Long-term retainage	[2]	1,410	1,506
Total retainage		$ 58,544	$ 46,615

[1] Expected to be paid within one year or less and included in receivables, net.

[2] Included in deferred charges and other assets - other.