Other (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leases And Other Property Plant And Equipment [Line Items]
Rig termination fee as reduced rental payments | $	$ 0	$ 0	$ 3,075
Horizontal Drilling Rig [Member]
Operating Leases And Other Property Plant And Equipment [Line Items]
Number of contracts | contract	5