Investment Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2017 USD ($) Security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) Security
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position (in security) | Security	119		132
Fair value of investments held to maturity pledged as collateral	$ 1,100,000,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	7 years 3 months
Number of security positions in the securities available for sale portfolio in an unrealized loss position (in security) | Security	288		298
Amortized cost	$ 1,470,374,000		$ 1,315,723,000
Available for sale	1,454,331,000		1,297,373,000
Gross unrealized losses	20,772,000		$ 22,416,000
Fair value of securities available for sale pledged as collateral	$ 547,500,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	9 years 1 month 2 days
Other than temporary impairment losses recognized in earnings	$ 0	$ 0
Previously Other-Than-Temporarily Impaired Securities | Trust Preferred Securities Subject to Mandatory Redemption
Investment Securities [Line Items]
Amortized cost	2,800,000
Available for sale	$ 2,000,000
Pooled Trust Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position (in security) | Security	2
Amortized cost	$ 7,900,000
Available for sale	6,400,000
Pooled Trust Preferred Securities | Investment Grade
Investment Securities [Line Items]
Gross unrealized losses	709,000
Four Private Label Mortgage-Backed Securities
Investment Securities [Line Items]
Amortized cost	9,700,000
Available for sale	$ 9,400,000
Single Issuer Trust Preferred Securities | Non-Rated
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position (in security) | Security	4