Revenue from Contracts with Customers Amortization of Deferred Revenues and Costs (Details) - Drilling Services [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Amortization of deferred revenues	$ 2,961	$ 2,400	$ 1,566
Amortization of deferred costs	$ 2,855	$ 4,953	$ 2,813