Leases (Schedule of lease costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Amortization of finance leased assets	$ 1,036	$ 995	$ 2,061	$ 1,980
Interest on finance lease liabilities	60	100	130	211
Operating lease cost	1,395	1,052	2,639	1,651
Short-term lease cost	2,751	12,038	6,742	22,012
Variable lease cost	83	84	165	190
Total lease cost	5,325	14,269	11,737	26,044
Capitalized costs included in short-term lease costs	$ 400	$ 9,000	$ 1,400	$ 14,700