Loans Receivable and Allowance for Loan Losses - Allowance for Loans, by Portfolio Segment and Impairment Method (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Positive or Negative Qualitative Adjustment of the Loss Migration Ratio or Individual Specific Reserve Allocations, In Basis Points	0.50%
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	$ 124,158		$ 116,269
Specific allowance	9,741		12,666
Loss coverage ratio	7.80%		10.90%
Non-impaired loans	5,224,158		4,960,074
General allowance	57,129		54,654
Loss coverage ratio	1.10%		1.10%
Total loans outstanding	5,348,316		5,076,343
Allowance for loan losses - Total	66,870	65,699	67,320	71,675	73,268	66,941
Loss coverage ratio	1.30%		1.30%
Real estate
Loans by Portfolio Segment and Impairment Method [Abstract]
Total loans outstanding	4,184,298		3,904,058
Real estate | Residential
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	0		0
Specific allowance	0		0
Loss coverage ratio	0.00%		0.00%
Non-impaired loans	10,019		10,039
General allowance	25		25
Loss coverage ratio	0.20%		0.20%
Total loans outstanding	10,019		10,039
Allowance for loan losses - Total	25		25
Loss coverage ratio	0.20%		0.20%
Real estate | Commercial
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	71,714		67,544
Specific allowance	3,825		6,670
Loss coverage ratio	5.30%		9.90%
Non-impaired loans	4,017,528		3,753,619
General allowance	42,096		39,227
Loss coverage ratio	1.00%		1.00%
Total loans outstanding	4,089,242		3,821,163
Allowance for loan losses - Total	45,921		45,897
Loss coverage ratio	1.10%		1.20%
Real estate | Construction
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	1,588		1,625
Specific allowance	0		0
Loss coverage ratio	0.00%		0.00%
Non-impaired loans	83,449		71,231
General allowance	401		628
Loss coverage ratio	0.50%		0.90%
Total loans outstanding	85,037		72,856
Allowance for loan losses - Total	401		628
Loss coverage ratio	0.50%		0.90%
Commercial business
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	40,413		40,106
Specific allowance	3,618		5,805
Loss coverage ratio	9.00%		14.50%
Non-impaired loans	888,730		908,987
General allowance	11,680		11,787
Loss coverage ratio	1.30%		1.30%
Total loans outstanding	929,143		949,093
Allowance for loan losses - Total	15,298		17,592
Loss coverage ratio	1.60%		1.90%
Trade finance
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	8,985		5,692
Specific allowance	2,298		159
Loss coverage ratio	25.60%		2.80%
Non-impaired loans	132,068		118,993
General allowance	2,270		2,494
Loss coverage ratio	1.70%		2.10%
Total loans outstanding	141,053		124,685
Allowance for loan losses - Total	4,568		2,653
Loss coverage ratio	3.20%		2.10%
Consumer and other
Loans by Portfolio Segment and Impairment Method [Abstract]
Impaired loans (gross carrying value)	1,458		1,302
Specific allowance	0		32
Loss coverage ratio	0.00%		2.50%
Non-impaired loans	92,364		97,205
General allowance	657		493
Loss coverage ratio	0.70%		0.50%
Total loans outstanding	93,822		98,507
Allowance for loan losses - Total	$ 657		$ 525
Loss coverage ratio	0.70%		0.50%