Notes Payable, Collateralized and Short-Term Borrowings - Summary of Interest Expense Related to Company's Convertible Notes (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Amortization of discount		$ (1,265)	$ (1,014)
4.50% Convertible Notes [Member]
Debt Instrument [Line Items]
Coupon interest	$ 1,800		3,600
Amortization of discount	1,234		2,459
Total interest expense	$ 3,034		$ 6,059