Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 119,788
Valuation Adjustment	6,542
Fair Value	$ 113,246
Auction Rate Preferred Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
US treasury rate	1.54%
Auction Rate Preferred Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Spread to US treasury rate	110.00%
Auction Rate Preferred Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Spread to US treasury rate	150.00%
Municipal Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Spread to US treasury rate	175.00%
US treasury rate	1.66%
Student Loan Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Spread to US treasury rate	1.20%
US treasury rate	2.10%
Auction Rate Securities Owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 91,975	[1]
Valuation Adjustment	5,173	[1]
Fair Value	86,802	[1]
Auction Rate Securities Owned | Auction Rate Preferred Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	87,925	[1]
Valuation Adjustment	4,550	[1]
Fair Value	$ 83,375	[1]
Valuation Technique	Discounted Cash Flow	[1]
Duration	4 years	[1]
Auction Rate Securities Owned | Auction Rate Preferred Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	1.70%	[1],[2]
Current Yield	0.44%	[1],[3]
Auction Rate Securities Owned | Auction Rate Preferred Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.32%	[1],[2]
Current Yield	0.85%	[1],[3]
Auction Rate Securities Owned | Auction Rate Preferred Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.00%	[1],[2]
Duration	4 years	[1]
Current Yield	0.64%	[1],[3]
Auction Rate Securities Owned | Municipal Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 25	[1]
Valuation Adjustment	2	[1]
Fair Value	$ 23	[1]
Valuation Technique	Discounted Cash Flow	[1]
Discount Rate	2.90%	[1],[4]
Duration	4 years 6 months	[1]
Current Yield	1.14%	[1],[3]
Observable trades in inactive market for in portfolio securities	83.62%	[1]
Auction Rate Securities Owned | Municipal Auction Rate Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.90%	[1],[4]
Duration	4 years 6 months	[1]
Current Yield	1.14%	[1],[3]
Observable trades in inactive market for in portfolio securities	83.62%	[1]
Auction Rate Securities Owned | Student Loan Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 400	[1]
Valuation Adjustment	27	[1]
Fair Value	$ 373	[1]
Valuation Technique	Discounted Cash Flow	[1]
Discount Rate	3.30%	[1],[5]
Duration	7 years	[1]
Current Yield	2.19%	[1],[3]
Auction Rate Securities Owned | Student Loan Auction Rate Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	3.30%	[1],[5]
Duration	7 years	[1]
Current Yield	2.19%	[1],[3]
Auction Rate Securities Owned | Other Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 3,625	[1],[6]
Valuation Adjustment	594	[1],[6]
Fair Value	$ 3,031	[1],[6]
Valuation Technique	Secondary Market Trading Activity	[1],[6]
ARS purchase commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 27,813	[1]
Valuation Adjustment	1,369	[1]
Fair Value	26,444	[1]
ARS purchase commitments | Auction Rate Preferred Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	27,766	[7]
Valuation Adjustment	1,366	[7]
Fair Value	$ 26,400	[7]
Valuation Technique	Discounted Cash Flow	[7]
Duration	4 years	[7]
ARS purchase commitments | Auction Rate Preferred Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	1.70%	[2],[7]
Current Yield	0.44%	[3],[7]
ARS purchase commitments | Auction Rate Preferred Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.32%	[2],[7]
Current Yield	0.85%	[3],[7]
ARS purchase commitments | Auction Rate Preferred Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.00%	[2],[7]
Duration	4 years	[7]
Current Yield	0.64%	[3],[7]
ARS purchase commitments | Municipal Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 2	[7]
Valuation Adjustment	0	[7]
Fair Value	$ 2	[7]
Valuation Technique	Discounted Cash Flow	[7]
Discount Rate	2.90%	[4],[7]
Duration	4 years 6 months	[7]
Current Yield	1.14%	[3],[7]
ARS purchase commitments | Municipal Auction Rate Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.90%	[4],[7]
Duration	4 years 6 months	[7]
Current Yield	1.14%	[3],[7]
ARS purchase commitments | Student Loan Auction Rate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Principal	$ 45	[7]
Valuation Adjustment	3	[7]
Fair Value	$ 42	[7]
Valuation Technique	Discounted Cash Flow	[7]
Discount Rate	3.30%	[5],[7]
Duration	7 years	[7]
Current Yield	2.19%	[3],[7]
ARS purchase commitments | Student Loan Auction Rate Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	3.30%	[5],[7]
Duration	7 years	[7]
Current Yield	2.19%	[3],[7]

[1] Principal amount represents the par value of the ARS and is included in securities owned in the consolidated balance sheet at December 31, 2015. The valuation adjustment amount is included as a reduction to securities owned in the consolidated balance sheet at December 31, 2015.

[2] Derived by applying a multiple to the spread between 110% to 150% to the U.S. Treasury rate of 1.54%.

[3] Based on current yields for ARS positions owned.

[4] Derived by applying a multiple to the spread of 175% to the U.S. Treasury rate of 1.66%.

[5] Derived by applying the sum of the spread of 1.20% to the U.S. Treasury rate of 2.10%.

[6] Represents ARS issued by a credit default obligation structure that the Company has purchased and is committed to purchase as a result of a legal settlement.

[7] Principal amount represents the present value of the ARS par value that the Company is committed to purchase at a future date. This principal amount is presented as an off-balance sheet item. The Valuation Adjustment amount is included in accounts payable and other liabilities on the consolidated balance sheet at December 31, 2015.