Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Recurring Fair Value Measurements
Residential loans held for sale	$ 30,077	$ 41,340
Derivative assets	62,056	47,764
Derivative liabilities	86,106	72,824
True Up Liability	11,551	12,061
Recurring [Member]
Recurring Fair Value Measurements
Available for sale securities	3,353,553	2,987,040
Residential loans held for sale	30,077	41,340
Derivative assets	62,056	47,764
Total assets at fair value on a recurring and nonrecurring basis	3,445,686	3,076,144
Derivative liabilities	86,106	72,824
True Up Liability	11,551	12,061
Total liabilities at fair value on a recurring basis	97,657	84,885
Level 1 [Member] | Recurring [Member]
Recurring Fair Value Measurements
Available for sale securities	3,299	3,922
Residential loans held for sale	0	0
Derivative assets	0	0
Total assets at fair value on a recurring and nonrecurring basis	3,299	3,922
Derivative liabilities	0	0
True Up Liability	0	0
Total liabilities at fair value on a recurring basis	0	0
Level 2 [Member] | Recurring [Member]
Recurring Fair Value Measurements
Available for sale securities	3,262,715	2,922,774
Residential loans held for sale	30,077	41,340
Derivative assets	62,056	47,764
Total assets at fair value on a recurring and nonrecurring basis	3,354,848	3,011,878
Derivative liabilities	86,106	72,824
True Up Liability	0	0
Total liabilities at fair value on a recurring basis	86,106	72,824
Level 3 [Member] | Recurring [Member]
Recurring Fair Value Measurements
Available for sale securities	87,539	60,344
Residential loans held for sale	0	0
Derivative assets	0	0
Total assets at fair value on a recurring and nonrecurring basis	87,539	60,344
Derivative liabilities	0	0
True Up Liability	11,551	12,061
Total liabilities at fair value on a recurring basis	$ 11,551	$ 12,061