Investment Securities Held to Maturity - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2013 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities at carrying value	$ 378,538,000	$ 343,127,000
Investment securities held to maturity	473,684,000	469,528,000
Fair value	488,331,000	482,473,000
Proceeds from the calls	$ 37,271,000	$ 41,057,000	$ 97,974,000
Number of securities in an unrealized loss position | security	99	163
Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Recognized gain on calls of securities held to maturity portfolio	$ 8,000	$ 23,000
Recognized loss on calls of securities held to maturity portfolio	0	0
Proceeds from the calls	26,973,000	15,156,000
Held-to-maturity Securities [Member] | Nonperforming Financing Receivable [Member]
Schedule of Held-to-maturity Securities [Line Items]
Proceeds from the calls		500,000
Gross realized loss on securities sold		3,000
Gross recognized gain (loss) on calls of securities		0
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	1,597,000	2,816,000
Fair value	$ 1,658,000	$ 2,939,000