Parent Guarantor - Schedule of Condensed Consolidating Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 101,980				$ 80,810
Operating expenses	(94,290)				(58,145)
General and administrative	(12,660)				(10,107)
Merger transaction expense	(2,414)				(4,763)
Interest Expense	(13,679)				(13,090)
Interest income and other income (expense)	(104,877)				(19,642)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	(125,940)				(24,937)
(Provision for) Benefit from Income Taxes	29,711				0
Equity in earnings (loss) of subsidiaries	0				0
Net Income (Loss)	(96,229)	$ 222,423	$ (29,360)	$ (46,906)	(24,937)
Intercompany Eliminations
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0				0
Operating expenses	0				0
General and administrative	0				0
Merger transaction expense	0				0
Interest Expense	0				0
Interest income and other income (expense)	0				0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0				0
(Provision for) Benefit from Income Taxes	0				0
Equity in earnings (loss) of subsidiaries	96,229				24,937
Net Income (Loss)	96,229				24,937
Parent Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0				0
Operating expenses	0				0
General and administrative	0				0
Merger transaction expense	0				0
Interest Expense	0				0
Interest income and other income (expense)	0				0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0				0
(Provision for) Benefit from Income Taxes	0				0
Equity in earnings (loss) of subsidiaries	(96,229)				(24,937)
Net Income (Loss)	(96,229)				(24,937)
Subsidiary Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating revenues	101,980				80,810
Operating expenses	(94,290)				(58,145)
General and administrative	(12,660)				(10,107)
Merger transaction expense	(2,414)				(4,763)
Interest Expense	(13,679)				(13,090)
Interest income and other income (expense)	(104,877)				(19,642)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	(125,940)				(24,937)
(Provision for) Benefit from Income Taxes	29,711				0
Equity in earnings (loss) of subsidiaries	0				0
Net Income (Loss)	$ (96,229)				$ (24,937)