Off Balance Sheet Arrangements and Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Minimum
Guarantees
Assessment rate for financial institutions in the lowest risk category (as a percent)	0.025%
Assessment rate for financial institutions in the highest risk category (as a percent)	0.30%
Maximum
Guarantees
Assessment rate for financial institutions in the lowest risk category (as a percent)	0.09%
Assessment rate for financial institutions in the highest risk category (as a percent)	0.45%
American Savings Bank (ASB)
Guarantees
FDIC insurance assessment	$ 3,000	$ 2,900
Indemnification Agreement | American Savings Bank (ASB)
Guarantees
Accrued indemnification litigation obligation	1,100
Home equity line of credit
Guarantees
Unused Commitments to Extend Credit	1,089,633	1,011,334
Commercial and commercial real estate
Guarantees
Unused Commitments to Extend Credit	526,133	527,987
Consumer loans
Guarantees
Unused Commitments to Extend Credit	56,312	58,080
Residential 1-4 family
Guarantees
Unused Commitments to Extend Credit	20,524	14,241
Commercial and financial standby letters of credit [Member]
Guarantees
Unused Commitments to Extend Credit	20,082	15,747
March 2011 Class Action Lawsuit
Guarantees
Tentative settlement amount	2,000
Loss contingency reserve	2,000
Reserve for Off-balance Sheet Activities [Member]
Guarantees
Unused Commitments to Extend Credit	$ 1,712,684	$ 1,627,389