Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Measurement Inputs, Disclosure [Line Items]
Transfers between Level 1 and 2	$ 0	$ 0
Own credit risk	0.45%	0.50%
Long-term forward rate assumption, minimum	25.00%
Long-term forward rate assumption, maximum	30.00%
Market based implied volatility inputs	5 years
Change in fair value, period	10 years
Standard and Poor's Composite Stock Price Index, Year 20
Fair Value, Measurement Inputs, Disclosure [Line Items]
Long-term forward rate assumption	23.40%	24.00%