401(k) Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employer Contribution Common Stock [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of specified salary amount matched by employer	50.00%
Percentage of employee salary eligible for matching	4.00%
Employer contributions	$ 1,194,000	$ 1,225,000	$ 1,098,000
Employer Contribution Cash [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of specified salary amount matched by employer	50.00%
Percentage of employee salary eligible for matching	4.00%
Employer contributions	$ 817,000	924,000	941,000
Certain Employees [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of employee salary eligible for matching	3.00%
Defined Benefit Plan, Union Employees [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 369,000	$ 358,000	$ 393,000