Investment Securities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) Security	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Security Segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Investment [Line Items]
Proceeds from sales of investment securities held-to-maturity				$ 855,000
Net securities gains	$ 1,856,000	$ 512,000	$ 2,962,000	3,195,000
Trading securities that consist of mutual funds	$ 4,838,000	$ 3,995,000	$ 4,838,000	3,995,000	$ 3,941,000
Number of segments | Segment			2
Other-than-temporary-impairment losses on securities			$ 0	0
Number of securities in security portfolio | Security	1,758		1,758
Number of securities in unrealized loss position | Security	94		94
Unrealized losses	$ 19,164,000		$ 19,164,000		31,608,000
Municipal Bonds [Member]
Investment [Line Items]
Proceeds from sales of investment securities held-to-maturity				800,000
Net securities gains				52,000
Former Directors and Executives [Member]
Investment [Line Items]
Trading securities that consist of mutual funds	$ 4,800,000		$ 4,800,000		3,900,000
Pooled Trust Preferred Securities, Not Subject to FASB ASC 325-10 [Member]
Investment [Line Items]
Number of trust preferred securities | Security	2		2
Securities portfolio at fair value	$ 6,500,000		$ 6,500,000
Unrealized losses	$ 7,400,000		$ 7,400,000
Pooled Trust Preferred Securities, Subject To FASB ASC 325-10 [Member]
Investment [Line Items]
Number of trust preferred securities | Security	1		1
Securities portfolio at fair value	$ 200,000		$ 200,000
Unrealized losses	$ 3,000,000		$ 3,000,000
Pooled Trust Preferred Securities [Member]
Investment [Line Items]
Number of trust preferred securities | Security	3		3
Securities portfolio at fair value	$ 6,700,000		$ 6,700,000
Unrealized losses			10,300,000
Unrealized losses	$ 10,339,000		10,339,000		$ 9,420,000
Other-than-temporary-impairment losses			$ 0	$ 0