Accounts Receivable (Tables)

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]

Accounts receivable consisted of the following at December 31: 

(in thousands)	2017			2016
Contract receivables	$	231,808		$	200,732
Contract retainages		42,732			32,486
Other		9,073			1,856
		283,613			235,074
Less: Allowance for doubtful accounts		(605	)		(432	)
	$	283,008		$	234,642

Schedule of Roll Forward Activity of Allowance for Doubtful Accounts [Table Text Block]

The roll-forward of activity in the allowance for doubtful accounts was as follows for the years ended December 31:

(in thousands)	2017			2016			2015
Balance at beginning of period	$	432		$	376		$	1,179
Less: Reduction in (provision for) allowances		(263	)		(146	)		528
Less: Write offs, net of recoveries		92			90			275
Change in foreign currency translation		(2	)		—			—
Balance at end of period	$	605		$	432		$	376