Basis of presentation and significant accounting policies - Other current liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Accrued compensation and benefits		$ 25,947	$ 14,342
Accrued interest payable		24,152	24,208
Purchased oil payable		17,213	12,189
Lease operating expense payable		10,572	13,205
Capital contribution payable to equity method investee	[1]	0	27,583
Other accrued liabilities		16,331	14,695
Total other current liabilities		$ 94,215	$ 106,222

[1] See Notes 14 and 15.a for additional discussion regarding the Company's equity method investee.