Notes Payable, Federal Home Loan Bank Advances, Other Borrowings, Secured Borrowings And Subordinated Notes (Narrative) (Detail) (USD $)	3 Months Ended		12 Months Ended		3 Months Ended					3 Months Ended					3 Months Ended		0 Months Ended	3 Months Ended						3 Months Ended				3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2010	Dec. 31, 2012	Mar. 31, 2013 Notes Payable to Banks [Member]	Mar. 31, 2013 Repurchase Agreements [Member]	Mar. 31, 2012 Repurchase Agreements [Member]	Mar. 31, 2013 Borrowings From Banks And Brokers [Member]	Mar. 31, 2012 Borrowings From Banks And Brokers [Member]	Mar. 31, 2013 Lender's Prime Rate [Member]	Mar. 31, 2013 Eurodollar Rate [Member]	Mar. 31, 2013 British Bankers Association's LIBOR Rate [Member]	Mar. 31, 2013 Great Lakes Advisors [Member]	Mar. 31, 2013 Agreement [Member]	Mar. 31, 2013 Federal Funds Rate [Member]	Dec. 07, 2010 Tangible Equity Units [Member]	Mar. 15, 2011 Junior Subordinated Debt [Member]	Mar. 31, 2013 Junior Subordinated Debt [Member]	Mar. 31, 2013 Fixed Rate Promissory Note [Member]	Jun. 30, 2012 Capital Unit, Class A [Member]	Mar. 31, 2012 Capital Unit, Class A [Member]	Sep. 30, 2009 Capital Unit, Class A [Member]	Mar. 31, 2013 Subordinated Debt [Member]	Mar. 31, 2013 Revolving Credit Facility [Member]	Mar. 31, 2013 Long-term Debt [Member]	Mar. 31, 2013 Unsecured Debt [Member]	Mar. 31, 2013 Subordinated Note Due May Twenty Nine Two Thousand And Fifteen [Member]	Jun. 30, 2012 Subordinated Note Due October Twenty Nine Two Thousand And Twelve [Member]	Jun. 30, 2012 Subordinated Note Due May One Two Thousand And Thirteen [Member]
Debt Instrument [Line Items]
Notes payable	$ 31,911,000	$ 52,639,000		$ 2,093,000	$ 31,000,000																					$ 911,000
Loan agreement with interest rate of unaffiliated banks					4.00%																					1.25%
Loan agreement with unaffiliated banks, amount	101,000,000																							100,000,000	1,000,000
Maturity date	Dec. 15, 2013		Dec. 15, 2013																					Oct. 25, 2013	Jun. 01, 2015
Notes payable														1,000										30,000,000
Percentage of commitment fee payment	0.50%
Federal Home Loan Bank advances, restructured advances		292,500,000
Federal Home Loan Bank advances, prepayment fees		22,400,000
Securities sold under repurchase agreements	224,297,000	384,046,000		238,401,000		44,300,000	81,600,000	180,000,000	302,500,000
Junior subordinated notes																44,700,000
Junior subordinated amortizing notes interest rate																		9.50%
Quarterly principal and interest payments																		4,300,000
Initial payment of subordinated notes																	4,600,000											5,000,000	10,000,000
Other	31,947,000	26,991,000		36,010,000														12,200,000	19,700,000
Contractual rate																			3.75%
Instruments issued by the securitization entity																						600,000,000
Incremental interest rate over base rate													1.00%									1.45%	1.30%
Repurchase amount																				67,200,000	172,000,000
Subordinated notes	15,000,000	35,000,000		15,000,000																							15,000,000
Subordinated debt, annual principal payment	$ 5,000,000
Borrowings Agreement Considered Base Rate Loans on Bear Interest Rate	4.00%									0.50%	1.50%				1.00%
Borrowings Agreement Considered Eurodollar Rate Loans on Bear Interest Rate	4.00%											3.00%