Fair Value Assumptions and Methodology for Assets and Liabilities (Detail)	Jun. 13, 2017	May 21, 2017	Dec. 31, 2016
Measurement Input, Risk Free Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input	1.51	1.78	1.93
Measurement Input, Price Volatility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input	88	89	98
Measurement Input, Expected Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input	4.6	4.6	5.0
Measurement Input, Expected Dividend Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input	0	0	0