Investment Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position | Security	132	74
Held to maturity, fair value	$ 1,925,572,000	$ 1,596,385,000
Fair value of investments held to maturity pledged as collateral	$ 968,000,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	6 years 8 months
Number of security positions in the securities available for sale portfolio in an unrealized loss position | Security	298	291
Amortized cost	$ 1,315,723,000	$ 1,516,937,000
Available for sale	1,297,373,000	1,506,861,000
Gross unrealized losses	22,416,000	$ 16,312,000
Fair value of securities available for sale pledged as collateral	$ 537,400,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	8 years 7 months
Corporate and other debt securities
Investment Securities [Line Items]
Number of held-to-maturity securities sold (in security) | Security		1
Held to maturity, fair value			$ 9,800,000
Single Issuer Trust Preferred Security | Non-Rated [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position | Security	4
Trust preferred securities
Investment Securities [Line Items]
Impairment charge part of combined amortized cost of the securities	$ 0	$ 0		$ 0
Three Private Label Mortgage-Backed Securities
Investment Securities [Line Items]
Other-than-temporarily impaired mortgage-backed securities, amortized cost	10,200,000
Other-than-temporarily impaired mortgage-backed securities, fair value	$ 9,900,000
Number of previously impaired securities (in security) | Security	4
Pooled Trust Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position | Security	2
Amortized cost	$ 10,200,000
Available for sale	$ 8,000,000
Pooled Trust Preferred Securities | Investment Grade
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position | Security	1
Gross unrealized losses	$ 1,300,000
Trust preferred securities
Investment Securities [Line Items]
Held to maturity, fair value	59,804,000	59,785,000
Amortized cost	10,164,000	10,458,000
Available for sale	8,009,000	8,404,000
Gross unrealized losses	$ 2,155,000	$ 2,054,000
Number of available for sale securities (in security) | Security	2	2
Other-than-temporarily impaired mortgage-backed securities, amortized cost	$ 2,800,000
Other-than-temporarily impaired mortgage-backed securities, fair value	$ 1,900,000
Number of previously impaired securities (in security) | Security	1
Obligations of states and political subdivisions
Investment Securities [Line Items]
Held to maturity, fair value	$ 566,590,000	$ 504,865,000
Amortized cost	120,741,000	125,002,000
Available for sale	119,767,000	124,966,000
Gross unrealized losses	1,191,000	$ 441,000
Obligations of states and political subdivisions | Other Than Temporarily Impaired Securities
Investment Securities [Line Items]
Amortized cost	20,300,000
Available for sale	$ 20,800,000
Investment carrying value percentage	43.00%
Investment carrying value	$ 686,400,000