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Subsequent Events - Additional Information (Detail) - USD ($)		9 Months Ended
	Oct. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Shares issued		2,000,000	15,000,000
Letter of Credit Facility [Member]
Subsequent Event [Line Items]
Available capacity under credit facility		$ 14,000,000,000
Subsequent Event [Member] \| Letter of Credit Facility [Member] \| Letter of Credit Agreement [Member]
Subsequent Event [Line Items]
Available capacity under credit facility	$ 230,000,000
Maturity period	3 years
Purchase Agreement [Member] \| 12% Redeemable Preferred Stock [Member] \| Purchasers [Member] \| Private Placement [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Shares issued	300,000
Stock percentage	12.00%
Warrant rights	3.75% times the total number of shares of our common stock outstanding
Warrants outstanding	$ 289,500,000
Warrants to purchase common stock, exercise price per share	$ 0.01