Fair Value Measurement of Assets and Liabilities - Recurring and Non-Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment securities
Available for sale	$ 1,447,737	$ 1,297,373
Non-recurring fair value measurements
Unpaid principal balances of loans held for sale	13,100	58,200
U.S. Treasury securities
Investment securities
Available for sale	50,148	49,591
U.S. government agency securities
Investment securities
Available for sale	44,230	23,041
Obligations of states and political subdivisions
Investment securities
Available for sale	118,402	119,767
Residential mortgage-backed securities
Investment securities
Available for sale	1,161,157	1,015,542
Trust preferred securities
Investment securities
Available for sale	5,393	8,009
Corporate and other debt securities
Investment securities
Available for sale	57,427	60,565
Equity securities
Investment securities
Available for sale	10,980	20,858
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements
Investment securities
Available for sale	59,148	58,961
Loans held for sale	0	0
Other assets	0	0
Total assets	59,148	58,961
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	50,148	49,591
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	7,890	8,064
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Equity securities
Investment securities
Available for sale	1,110	1,306
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	0	0
Loan servicing rights	0	0
Foreclosed assets	0	0
Total	0	0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements
Investment securities
Available for sale	1,378,792	1,226,524
Loans held for sale	13,321	57,708
Other assets	26,696	29,055
Total assets	1,418,809	1,313,287
Liabilities
Other liabilities	23,868	44,077
Total liabilities	23,868	44,077
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	0	0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	44,230	23,041
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	118,402	119,767
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	1,153,475	1,005,589
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	3,278	6,074
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	49,537	52,501
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Equity securities
Investment securities
Available for sale	9,870	19,552
Significant Other Observable Inputs (Level 2) \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	0	0
Loan servicing rights	0	0
Foreclosed assets	0	0
Total	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements
Investment securities
Available for sale	9,797	11,888
Loans held for sale	0	0
Other assets	0	0
Total assets	9,797	11,888
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	7,682	9,953
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	2,115	1,935
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Equity securities
Investment securities
Available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	33,260	5,385
Loan servicing rights	7,072	6,489
Foreclosed assets	1,762	4,532
Total	42,094	16,406
Fair Value \| Recurring fair value measurements
Investment securities
Available for sale	1,447,737	1,297,373
Loans held for sale	13,321	57,708
Other assets	26,696	29,055
Total assets	1,487,754	1,384,136
Liabilities
Other liabilities	23,868	44,077
Total liabilities	23,868	44,077
Fair Value \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	50,148	49,591
Fair Value \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	44,230	23,041
Fair Value \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	118,402	119,767
Fair Value \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	1,161,157	1,015,542
Fair Value \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	5,393	8,009
Fair Value \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	57,427	60,565
Fair Value \| Recurring fair value measurements \| Equity securities
Investment securities
Available for sale	10,980	20,858
Fair Value \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	33,260	5,385
Loan servicing rights	7,072	6,489
Foreclosed assets	1,762	4,532
Total	$ 42,094	$ 16,406

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Fair value of the collateral dependent impaired loans.

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