Comprehensive income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Available for sale ("AFS") investment securities with other-than-temporary impairment ("OTTI"):
Unrealized holding losses, net, net, before-tax amount	$ (8,242)	$ 7,930
Unrealized holding losses, net, income taxes	3,235	(3,108)
Unrealized holding losses, net, net of tax amount	(5,007)	4,822
Less: OTTI charges recognized in net income, before tax amount	(7,676)	(7,541)
Less: OTTI charges recognized in net income, income taxes	3,013	2,949
Less: OTTI charges recognized in net income, net	(4,663)	(4,592)
Net change for AFS investment securities with OTTI, before tax	(566)	15,471
Net change for AFS investment securities with OTTI, income taxes	222	(6,057)
Net change for AFS investment securities with OTTI, after tax	(344)	9,414
AFS investment securities - all other:
Unrealized holding gains during period, net, before-tax amount	29,695	31,577
Unrealized holding gains during period, net, income taxes	(11,614)	(12,372)
Unrealized holding gains during period, net, net of tax amount	18,081	19,205
Less: reclassification adjustment for gains realized in net income, before-tax amount	45	39,353
Less: Reclassification adjustment for gains realized in net income, income taxes	(15)	(15,413)
Less: Reclassification adjustment for gains realized in net income, net	30	23,940
Net change for AFS investment securities - all other, before tax	29,650	(7,776)
Net change for AFS investment securities - all other, tax	(11,599)	3,041
Net change for AFS investment securities - all other, after tax	18,051	(4,735)
Held-to-maturity ("HTM") investment securities with OTTI:
Unrealized holding gains on HTM securities, net, before-tax amount	(1,843)	(8,355)
Unrealized holding gains on HTM securities, net, income taxes	723	3,279
Unrealized holding gains on HTM securities, net, net of tax amount	(1,120)	(5,076)
Less: reclassification to income of unrealized holding losses, before tax	(819)	230
Less: reclassification to income of unrealized holding losses, tax	321	(90)
Less: reclassification to income of unrealized holding losses, net of tax	(498)	140
Less: OTTI charges recognized in net income, before tax	(3,810)	(8,500)
Less: OTTI charges recognized in net income, tax	1,495	3,336
Less: OTTI charges recognized in net income, net of tax	(2,315)	(5,164)
Net change for HTM investment securities with OTTI, before tax	2,786	(85)
Net change for HTM investment securities with OTTI, tax	(1,093)	33
Net change for HTM investment securities with OTTI, net of tax	1,693	(52)
Unrealized holding losses on investment securities previously transferred from AFS to HTM
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, before tax	1,123	1,698
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, Tax	(441)	(667)
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, net of tax	682	1,031
Net unrealized gains (losses) on investment securities, before tax	32,993	9,308
Net unrealized gains (losses) on investment securities, income taxes	(12,911)	(3,650)
Net unrealized gains (losses) on investment securities, net of tax	20,082	5,658
Reclassification to income for amortization of gains on terminated cash flow hedges , before tax	(112)	(112)
Reclassification to income for amortization of gains on terminated cash flow hedges, income taxes	42	42
Reclassification to income for amortization of gains on terminated cash flow hedges	(70)	(70)
Foreign currency translation adjustment, before tax	622
Foreign currency translation adjustment, tax	(220)
Foreign currency translation adjustment, net of tax	402
Defined benefit plans liability adjustment, before-tax amount	7,850	3,475
Defined benefit plans liability adjustment, income taxes	(3,081)	(1,364)
Defined benefit plans liability adjustment, net	4,769	2,111
Total Comprehensive Income, before-tax amount	41,353	12,671
Total Comprehensive Income, income taxes	(16,170)	(4,972)
Total other comprehensive income	$ 25,183	$ 7,699