Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	[1]
Valuation Allowance [Line Items]
Balance, beginning of period	$ 158,046	$ 158,290
Charge-offs	(6,991)	(5,830)
Recoveries	514	203
Balance, end of period	161,140	154,450
Non-Covered Loans
Valuation Allowance [Line Items]
Provision for (recovery of) non-covered loan losses	9,571	1,787
Mortgage Receivable
Valuation Allowance [Line Items]
Balance, beginning of period	128,275	125,416
Charge-offs	(5,411)
Recoveries	110	115
Balance, end of period	129,135	121,852
Mortgage Receivable | Non-Covered Loans
Valuation Allowance [Line Items]
Provision for (recovery of) non-covered loan losses	6,161	(3,679)
Other loans
Valuation Allowance [Line Items]
Balance, beginning of period	29,771	32,874
Charge-offs	(1,580)	(5,830)
Recoveries	404	88
Balance, end of period	32,005	32,598
Other loans | Non-Covered Loans
Valuation Allowance [Line Items]
Provision for (recovery of) non-covered loan losses	$ 3,410	$ 5,466

[1] Represents allowance for losses on non-covered loans, excluding PCI loans.