Activity in Allowance for Losses on Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Valuation Allowance [Line Items]
Balance, beginning of period	$ 45,481	$ 64,069	$ 64,069
Provision for (recovery of) losses on covered loans	7	(14,630)	(14,630)
Transfer to the allowance for losses on non-covered loans	(2,416)
Balance, end of period	43,942	49,439	45,481
Covered
Valuation Allowance [Line Items]
Provision for (recovery of) losses on covered loans	$ 877	$ (14,630)