Investment Securities - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Dec. 31, 2013 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Public offering redemption shares percentage		39.00%
Available for sale securities, fair value		$ 294,599,000	$ 341,523,000
Available for sale securities, adjusted cost basis		297,001,000	$ 345,342,000
Other-than-temporary impairment securities sold	$ 0	644,000
Unrealized other-than-temporary impairment due to credit losses	23,000	64,000
Net realized losses related to credit issues (i.e. principal reduced without a receipt of cash)	224,000	221,000
Unrealized losses on U.S. government sponsored and federal agency obligations, corporate stocks and bonds and Ginnie Mae ("GNMA") mortgage-backed securities as of June 30, 2012 due to changes in interest rates and other non-credit related factors totaled	$ 3,200,000	$ 4,200,000
Number of available for sale securities in a continuous unrealized loss position (in security) | security	34	63
Number of held to maturity securities in a continuous unrealized loss position (in security) | security			4
Investment securities with a fair value		$ 294,599,000	$ 341,523,000
Other-than-temporarily impaired
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, fair value		0	0
Other-than-temporary impairment securities sold		37,000
Other-than-temporarily impaired | Non-agency CMOs
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, fair value		0
Investment Securities
Schedule of Available-for-sale Securities [Line Items]
Investment securities with a fair value		$ 121,500,000	$ 92,300,000