Income Taxes - Reconciliation of Effective Tax Rate to Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Income Tax Rate [Line Items]
Net income (loss) before income taxes	$ 97,683	$ (61,106)
Tax expense (benefit) computed at statutory rate	20,513	(20,776)
Noncontrolling interest	(11,475)	12,118
Non-deductible general and administrative expenses	94	168
Return to accrual	0	(486)
Refundable tax credits	(505)	0
State income taxes, net of Federal benefit	1,208	(191)
Valuation allowance	(7,393)	(15,477)
Federal rate change	0	7,824
State rate change	28	445
Rate differential on Canadian activity	0	2
Total income tax expense (benefit)	$ 2,470	$ (16,373)
Effective tax rate (as a percent)	2.50%	26.80%
U.S.
Reconciliation Of Income Tax Rate [Line Items]
Net income (loss) before income taxes	$ 97,683	$ (61,082)
Statutory rate (as a percent)	21.00%	34.00%
Tax expense (benefit) computed at statutory rate	$ 20,513	$ (20,768)
Noncontrolling interest	(11,475)	12,118
Non-deductible general and administrative expenses	94	168
Return to accrual	0	(486)
Refundable tax credits	(505)	0
State income taxes, net of Federal benefit	1,208	(191)
Valuation allowance	(7,393)	(15,483)
Federal rate change	0	7,824
State rate change	28	445
Rate differential on Canadian activity	0	0
Total income tax expense (benefit)	$ 2,470	$ (16,373)
Effective tax rate (as a percent)	2.50%	26.80%
Canada
Reconciliation Of Income Tax Rate [Line Items]
Net income (loss) before income taxes	$ 0	$ (24)
Statutory rate (as a percent)	27.00%	26.00%
Tax expense (benefit) computed at statutory rate	$ 0	$ (8)
Noncontrolling interest	0	0
Non-deductible general and administrative expenses	0	0
Return to accrual	0	0
Refundable tax credits	0	0
State income taxes, net of Federal benefit	0	0
Valuation allowance	0	6
Federal rate change	0	0
State rate change	0	0
Rate differential on Canadian activity	0	2
Total income tax expense (benefit)	$ 0	$ 0
Effective tax rate (as a percent)	0.00%	0.00%