Initial Fair Value of Assets Obtained as Proceeds from Residential Mortgage Loans Securitized (Detail) (Residential Mortgage, USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Assets
Assets obtained as proceeds from loans securitized	$ 270,415	$ 209,801	$ 604,956	$ 418,598
Available-for-sale Securities
Assets
Assets obtained as proceeds from loans securitized				2,810
Available-for-sale Securities | Fair Value, Inputs, Level 3
Assets
Assets obtained as proceeds from loans securitized				2,810
Available-for-sale Securities | Fair Value, Inputs, Level 3 | Mortgage-backed securities - GNMA
Assets
Assets obtained as proceeds from loans securitized				2,810
Available-for-sale Securities | Mortgage-backed securities - GNMA
Assets
Assets obtained as proceeds from loans securitized				2,810
Servicing Asset At Fair Value Amount
Assets
Assets obtained as proceeds from loans securitized	4,890	3,794	10,839	7,535
Servicing Asset At Fair Value Amount | Fair Value, Inputs, Level 3
Assets
Assets obtained as proceeds from loans securitized	4,890	3,794	10,839	7,535
Fair Value, Inputs, Level 2
Assets
Assets obtained as proceeds from loans securitized	265,525	203,489	594,117	404,106
Fair Value, Inputs, Level 2 | Trading account securities
Assets
Assets obtained as proceeds from loans securitized	265,525	203,489	594,117	404,106
Fair Value, Inputs, Level 2 | Trading account securities | Mortgage-backed securities - GNMA
Assets
Assets obtained as proceeds from loans securitized	217,296	165,675	472,870	327,600
Fair Value, Inputs, Level 2 | Trading account securities | Mortgage-backed securities - FNMA
Assets
Assets obtained as proceeds from loans securitized	48,229	37,814	121,247	76,506
Fair Value, Inputs, Level 3
Assets
Assets obtained as proceeds from loans securitized	4,890	6,312	10,839	14,492
Fair Value, Inputs, Level 3 | Trading account securities
Assets
Assets obtained as proceeds from loans securitized		2,518		4,147
Fair Value, Inputs, Level 3 | Trading account securities | Mortgage-backed securities - GNMA
Assets
Assets obtained as proceeds from loans securitized		2,518		4,147
Trading account securities
Assets
Assets obtained as proceeds from loans securitized	265,525	206,007	594,117	408,253
Trading account securities | Mortgage-backed securities - GNMA
Assets
Assets obtained as proceeds from loans securitized	217,296	168,193	472,870	331,747
Trading account securities | Mortgage-backed securities - FNMA
Assets
Assets obtained as proceeds from loans securitized	$ 48,229	$ 37,814	$ 121,247	$ 76,506