Class A Redeemable Convertible Preferred Stock - Schedule of Components of Series A Preferred Stock, Separately for Shares Redeemed and for Shares Remaining, After Redemption and Loss on Redemption (Parenthetical) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Payments for repurchase of redeemable convertible preferred stock	$ 55.0