Employee Retirement Plans (Schedule of Contributions Made by the Company to Each Multiemployer Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Contributions	$ 292	$ 296	$ 333
National Integrated Group Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions	220	218	246
Sheet Metal Workers National Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions	42	50	56
Sheet Metal Workers Pension Plan Of Northern California
Defined Benefit Plan Disclosure [Line Items]
Contributions	$ 30	$ 28	$ 31