Parent Guarantor - Schedule of Condensed Consolidating Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 107,584				$ 110,398		$ 209,564	$ 191,208
Operating expenses	(102,300)				(75,725)		(196,590)	(133,870)
General and administrative	(12,401)				(11,624)		(25,061)	(21,731)
Merger transaction expense	0				(1,277)		(2,414)	(6,040)
Interest Expense	(14,381)				(13,093)		(28,060)	(26,183)
Interest income and other income (expense)	19,698				(55,585)		(85,179)	(75,227)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	(1,800)				(46,906)		(127,740)	(71,843)
(Provision for) Benefit from Income Taxes	(110)				0		29,601	0
Equity in earnings (loss) of subsidiaries	0				0		0	0
Net Income (Loss)	(1,910)	$ (96,229)	$ 222,423	$ (29,360)	(46,906)	$ (24,937)	(98,139)	(71,843)
Intercompany Eliminations
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0				0		0	0
Operating expenses	0				0		0	0
General and administrative	0				0		0	0
Merger transaction expense	0				0		0	0
Interest Expense	0				0		0	0
Interest income and other income (expense)	0				0		0	0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0				0		0	0
(Provision for) Benefit from Income Taxes	0				0		0	0
Equity in earnings (loss) of subsidiaries	1,910				46,906		98,139	71,843
Net Income (Loss)	1,910				46,906		98,139	71,843
Parent Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0				0		0	0
Operating expenses	0				0		0	0
General and administrative	0				0		0	0
Merger transaction expense	0				0		0	0
Interest Expense	0				0		0	0
Interest income and other income (expense)	0				0		0	0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0				0		0	0
(Provision for) Benefit from Income Taxes	0				0		0	0
Equity in earnings (loss) of subsidiaries	(1,910)				(46,906)		(98,139)	(71,843)
Net Income (Loss)	(1,910)				(46,906)		(98,139)	(71,843)
Subsidiary Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating revenues	107,584				110,398		209,564	191,208
Operating expenses	(102,300)				(75,725)		(196,590)	(133,870)
General and administrative	(12,401)				(11,624)		(25,061)	(21,731)
Merger transaction expense	0				(1,277)		(2,414)	(6,040)
Interest Expense	(14,381)				(13,093)		(28,060)	(26,183)
Interest income and other income (expense)	19,698				(55,585)		(85,179)	(75,227)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	(1,800)				(46,906)		(127,740)	(71,843)
(Provision for) Benefit from Income Taxes	(110)				0		29,601	0
Equity in earnings (loss) of subsidiaries	0				0		0	0
Net Income (Loss)	$ (1,910)				$ (46,906)		$ (98,139)	$ (71,843)