Capital Stock and Derivative Instruments - Schedule of Vesting Shares Subject to Repurchase (Detail) - Restricted shares subject to repurchase [Member] - shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amortization Expense [Line Items]
Unvested shares	4,039,591	4,197,396	1,343,764	1,456,987
1st quarter 2017 [Member]
Amortization Expense [Line Items]
Unvested shares	278,095
1st quarter 2018 [Member]
Amortization Expense [Line Items]
Unvested shares	3,690,576
1st quarter 2019 [Member]
Amortization Expense [Line Items]
Unvested shares	70,920