Revenues - Disaggregation of revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of revenue:
Total revenues	$ 598,302	$ 1,222,409	$ 1,721,005
Oilfield services transferred at a point in time
Disaggregation of revenue:
Total revenues	0	0	0
Oilfield services transferred over time
Disaggregation of revenue:
Total revenues	$ 598,302	$ 1,222,409	$ 1,721,005