Fair Value Disclosures of Financial Assets and Liabilities - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities measured at fair value	$ 0	$ 0
Available for sale of securities, fair value	841,706,000	817,115,000
Minimum discount rate on appraisals of collateral securing loan	10.00%
Maximum discount rate on appraisals of collateral securing loan	50.00%
Valuation allowance on impaired loans	4,400,000	4,900,000
Federal Agency Debentures [Member] | AAA-Rated [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale of securities, fair value	0
Federal Agency MBS [Member] | AAA-Rated [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale of securities, fair value	37,000,000
Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale of securities, fair value	692,100,000
Reverse Mortgage Trust [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale of securities, fair value	112,600,000
Impaired Loans (Collateral Dependent) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral for collateral dependent loans	41,439,000	38,379,000
Impaired Loans (Collateral Dependent) [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral for collateral dependent loans	$ 41,439,000	$ 38,379,000