Unearned ESOP Shares - Interest Paid on ESOP Loan and Dividends Received on Unallocated Shares (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Interest paid on ESOP loan	$ 18,943	$ 23,022	$ 31,597
Dividends on unallocated shares			19
ESOP [Member]
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Interest paid on ESOP loan			$ 13