Notes Payable, Federal Home Loan Bank Advances, Other Borrowings, Secured Borrowings And Subordinated Notes (Narrative) (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended			9 Months Ended		9 Months Ended							9 Months Ended						0 Months Ended		0 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2010	Dec. 31, 2011	Oct. 28, 2011	Sep. 30, 2012 Agreement [Member]	Nov. 08, 2012 Previous Borrowing Capacity [Member]	Sep. 30, 2012 Great Lakes Advisors [Member]	Sep. 30, 2012 Federal Funds Rate [Member]	Sep. 30, 2012 Lender's Prime Rate [Member]	Sep. 30, 2012 Eurodollar Rate [Member]	Sep. 30, 2012 British Bankers Association's LIBOR Rate [Member]	Sep. 30, 2012 Tangible Equity Units [Member]	Dec. 07, 2010 Tangible Equity Units [Member]	Sep. 30, 2012 Junior Subordinated Debt [Member]	Sep. 30, 2012 Fixed Rate Promissory Note [Member]	Jun. 30, 2012 October 2002 [Member]	Jun. 30, 2012 April 2003 [Member]	Sep. 30, 2012 October 2005 [Member]	Sep. 30, 2012 Capital Unit, Class A [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] Agreement [Member]	Nov. 08, 2012 Amended and Restated Credit Agreement [Member] Agreement [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] Term Loan [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] Federal Funds Rate [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] Lender's Prime Rate [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] Eurodollar Rate [Member]	Oct. 26, 2012 Amended and Restated Credit Agreement [Member] British Bankers Association's LIBOR Rate [Member]	Oct. 28, 2011 Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Notes payable			$ 2,275,000	$ 3,004,000		$ 52,822,000		$ 1,000
Notes payable outstanding										1,300,000														1,000,000
Incremental interest rate over base rate			1.30%					4.50%		1.00%	1.00%	0.50%	1.50%	3.50%								1.45%				1.00%	0.50%	1.50%	3.00%
Loan agreement with unaffiliated banks, amount			76,000,000
Revolving note			75,000,000
Restated credit agreement revolving credit facility, maturity date							2012-10-26																							October 26, 2012
Amount of Term Loan Agreement			1,000,000
Maturity Date			Dec. 15, 2013		Dec. 15, 2013																				Jun. 01, 2015
Line of credit facility, amount outstanding									0
Incremental interest rate over base rate								4.50%		1.25%													4.00%
Fixed Rate Promissory Note Interest Rate																		3.75%
Loans Payable																		20,000,000
Federal Home Loan Bank advances, restructured advances			292,500,000
Federal Home Loan Bank advances, prepayment fees			22,400,000
Customer balances in sweep accounts			70,800,000
Short-term borrowings from brokers			266,600,000
Junior subordinated notes															19,800,000	44,700,000
Junior subordinated amortizing notes interest rate																	9.50%
Quarterly principal and interest payments																	4,300,000
Initial payment of subordinated notes			20,000,000	10,000,000													4,600,000
Instruments issued by the securitization entity																						600,000,000
Company repurchased notes	67,200,000	172,000,000
Subordinated notes			15,000,000	40,000,000		35,000,000													5,000,000	10,000,000	15,000,000
Subordinated debt, annual principal payment			$ 5,000,000