Restricted Cash (Narrative) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Surety, Payment and Performance Bonds [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Surety, payment and performance bonds	$ 40,500,000	$ 39,500,000
Collateral	0	0
Workers Compensation Policy [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Collateral	$ 2,200,000	$ 2,500,000