Fair Value of Financial Instruments Quantitative Information About Significant Unobservable Inputs (Detail) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Equity Warrant Asset, Private Portfolio | Other Assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 128,049	$ 133,382
Valuation Technique	Modified Black-Scholes option pricing model	Modified Black-Scholes option pricing model
Volatility	36.90%	36.00%
Risk-Free interest rate	1.30%	1.10%
Marketability discount	17.10%	16.60%
Remaining Life Assumption	45.00%	45.00%
Equity Warrant Asset, Public Portfolio | Other Assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 764	$ 1,786
Valuation Technique	Modified Black-Scholes option pricing model	Modified Black-Scholes option pricing model
Sales Restrictions Discount	17.70%	18.00%
Volatility	46.60%	38.10%
Risk-Free interest rate	2.10%	2.10%
Other venture capital investments | Fair value accounting
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,040	$ 2,040
Valuation Technique	Private company equity pricing	Private company equity pricing