Capital Stock and Derivative Instruments - Schedule of Vesting Shares Subject to Repurchase (Detail) - Restricted shares subject to repurchase [Member] - shares	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortization Expense [Line Items]
Unvested shares	4,053,640	4,039,591	4,197,396
1st quarter 2018 [Member]
Amortization Expense [Line Items]
Unvested shares	3,774,684
1st quarter 2019 [Member]
Amortization Expense [Line Items]
Unvested shares	167,848
1st quarter 2020 [Member]
Amortization Expense [Line Items]
Unvested shares	111,108