Loans and Allowance for Loan Losses - Summary of Purchased Credit-Impaired Loans, Information Identified in Corporation's Acquisition of OBA and BCSB (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Feb. 15, 2014	Sep. 19, 2014
BCSB Bancorp, Inc. (BCSB) [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance		$ 10,470
Carrying amount		4,340
Allowance for loan losses	0	0
Impairment recognized since acquisition	276
Allowance reduction recognized since acquisition	0	0
OBA Financial Services, Inc. (OBA) [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	4,392		6,209
Carrying amount	2,136		2,826
Allowance for loan losses	0		0
Allowance reduction recognized since acquisition	$ 0		$ 0