Variable Interest Entities - Quantitative Inputs and Assumptions Used for Investments at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,736,703	$ 1,744,412
Valuation Techniques	Discounted cash flow
Fair Value, Measurements, Recurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	57,169
Fair Value, Measurements, Recurring [Member] | Bank Debt Term Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	56,566
Valuation Techniques	Discounted Cash Flow - Comparable Yields
Unobservable Inputs	Discount Rates
Range, Minimum	10.70%
Range, Maximum	30.40%
Weighted Average	15.70%
Fair Value, Measurements, Recurring [Member] | Common Stock [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 603
Valuation Techniques	Market Comparable Companies
Unobservable Inputs	Comparable Multiples
Stock, Range Minimum	6.6
Stock, Range Maximum	6.6
Stock, Weighted Average	6.6