Fair Value of Financial Instruments - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Measurement Inputs, Disclosure [Line Items]
Own credit risk	0.50%	0.40%
Long-term forward rate assumption	25.00%	25.00%
Market based implied volatility inputs	5 years
Standard and Poor's Composite Stock Price Index, Year 20
Fair Value, Measurement Inputs, Disclosure [Line Items]
Long-term forward rate assumption	24.40%	24.20%