Fair value (Estimated fair value and carrying value) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Assets,Carrying Value [Abstract]
Total cash and cash equivalents	$ 464,579		$ 591,487	$ 281,029		$ 448,946
Securities Purchased under Agreements to Resell	225,000		0
Trading Securities	214		180
Investment securities available-for-sale	2,612,839		2,959,912
Held-to-maturity Securities	895,500		884,026
Federal Home Loan Bank (FHLB) stock	22,868		23,779
Non-covered loans, net	1,137,918		1,142,978
Covered loans, net	447,720		496,276
Derivative Assets	11,367		9,317
FDIC Indemnification Asset	359,767		392,367	440,633		471,872
Accrued interest receivable	17,258		20,182
Servicing Assets	10,776	10,725	10,454	9,840	9,963	9,695
Liabilities,Carrying Valuu Disclosure [Abstract]
Derivative Liabilities	56,217		47,425
Deposits, Total	2,222,942		2,435,185
Securities Sold under Agreements to Repurchase	3,050,000		3,050,000
Advances from FHLB	285,070
FDIC-guaranteed term notes	0		105,834
Subordinated capital notes	36,083		36,083
Accrued expenses and other liabilities	27,686		35,602
Assets, Fair Value Disclosure [Abstract]
Available for sale Fair Value	2,612,839		2,959,912
Federal Home Loan Bank (FHLB) stock	22,868		23,779
Derivative Assets	11,367		9,317
Servicing Assets	10,776	10,725	10,454	9,840	9,963	9,695
Fair Value, Inputs, Level 1 [Member]
Assets,Carrying Value [Abstract]
Total cash and cash equivalents	464,579		591,487
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	464,579		591,487
Fair Value, Inputs, Level 2 [Member]
Assets,Carrying Value [Abstract]
Securities Purchased under Agreements to Resell	225,000		0
Trading Securities	214		180
Investment securities available-for-sale	2,575,543		2,959,912
Held-to-maturity Securities	895,500		884,026
Federal Home Loan Bank (FHLB) stock	22,868		23,779
Liabilities,Carrying Valuu Disclosure [Abstract]
Derivative Liabilities	56,217		47,425
Assets, Fair Value Disclosure [Abstract]
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure	225,000		0
Trading Securities, Fair Value Disclosure	214		180
Available for sale Fair Value	2,575,543		2,959,912
Held-to-maturity Securities, Fair Value Disclosure	925,266		904,556
Federal Home Loan Bank (FHLB) stock	22,868		23,779
Fair Value, Inputs, Level 3 [Member]
Assets,Carrying Value [Abstract]
Investment securities available-for-sale	37,296		47,312
Non-covered loans, net	1,172,636		1,169,917
Covered loans, net	447,720		496,276
Derivative Assets	11,367		9,317
FDIC Indemnification Asset	359,767		392,367
Accrued interest receivable	17,258		20,182
Servicing Assets	10,776		10,454
Liabilities,Carrying Valuu Disclosure [Abstract]
Deposits, Total	2,222,942		2,435,187
Securities Sold under Agreements to Repurchase	3,053,865		3,056,238
Advances from FHLB	286,653		281,753
FDIC-guaranteed term notes	0		105,834
Subordinated capital notes	36,083		36,083
Accrued expenses and other liabilities	27,686		35,602
Assets, Fair Value Disclosure [Abstract]
Available for sale Fair Value	37,296		47,312
Non-covered loans, net	1,188,608		1,211,539
Covered loans, net	524,603		584,110
Derivative Assets	11,367		9,317
FDIC shared-loss indemnification asset	274,847		312,957
Accrued interest receivable	17,258		20,182
Servicing Assets	10,776		10,454
Liabilities, Fair Value Disclosure [Abstract]
Deposits, Fair Value Disclosure	2,328,775		2,567,352
Securities sold under agreements to repurchase	3,124,827		3,092,122
Advances from FHLB	288,958		285,663
FDIC-guaranteed term notes	0		105,752
Subordinated capital notes	36,228		36,235
Accrued expenses and other liabilities	$ 27,686		$ 35,602