Notes Payable, Warrants and Subordinated Borrowings - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands		6 Months Ended
	Aug. 21, 2008	Jun. 30, 2015	Dec. 31, 2014
Notes Payable And Warrants [Line Items]
Subordinated Borrowings		$ 22,550,000	$ 22,550,000
Subordinated Borrowing, Interest Rate (as a percent)		5.50%
Class A [Member]
Notes Payable And Warrants [Line Items]
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.01	$ 0.01
Maximum percent of voting securities and total shares of class A common stock owned by holder or group of affiliates for warrant transfer (as a percent)		2.00%
Class A [Member] | Maximum [Member]
Notes Payable And Warrants [Line Items]
Percent of outstanding shares of common stock owned by holder or group of affiliates for warrant transfer (as a percent)		25.00%
Class A [Member] | Warrant [Member]
Notes Payable And Warrants [Line Items]
Warrants to purchase Class A shares (in shares)	5,455
Class A Shares purchase price per share (in dollars per share)	$ 22.00
Senior Notes [Member]
Notes Payable And Warrants [Line Items]
Senior Notes	$ 120,000,000
Senior Notes coupon interest (as a percent)	5.20%
Senior notes effective yield (as a percent)		7.94%
Redemption period (in days)		90 days
Event of default under the indenture accreted amount due and payable (as a percent)		33.33%
Maximum percent of aggregate principal amount of senior notes owned by holder or group of affiliates for transfer (as a percent)		15.00%