Fair Value Measurement of Assets and Liabilities - Recurring and Non-Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment securities
Available for sale	$ 1,749,001	$ 1,493,905
Non-recurring fair value measurements
Unpaid principal balances of loans held for sale	31,400	14,800
U.S. Treasury securities
Investment securities
Available for sale	48,363	49,642
U.S. government agency securities
Investment securities
Available for sale	36,513	42,505
Obligations of states and political subdivisions
Investment securities
Available for sale	205,237	112,884
Residential mortgage-backed securities
Investment securities
Available for sale	1,412,849	1,223,295
Trust preferred securities
Investment securities
Available for sale	1,590	3,214
Corporate and other debt securities
Investment securities
Available for sale	44,449	51,164
Equity securities
Investment securities
Available for sale		11,201
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements
Investment securities
Available for sale	55,950
Available-for-sale		58,807
Loans held for sale	0	0
Other assets	0	0
Total assets	55,950	58,807
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	48,363
Available-for-sale		49,642
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
Available-for-sale		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
Available-for-sale		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
Available-for-sale		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	0
Available-for-sale		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	7,587
Available-for-sale		7,783
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Equity securities
Investment securities
Available-for-sale		1,382
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	1,686,873
Available-for-sale		1,427,738
Loans held for sale	31,675	15,119
Other assets	28,539	26,417
Total assets	1,747,087	1,469,274
Liabilities
Other liabilities	44,917	24,330
Total liabilities	44,917	24,330
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	0
Available-for-sale		0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	36,513
Available-for-sale		42,505
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	205,237
Available-for-sale		112,884
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	1,406,671
Available-for-sale		1,215,935
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	1,590
Available-for-sale		3,214
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	36,862
Available-for-sale		43,381
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Equity securities
Investment securities
Available-for-sale		9,819
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	6,178
Available-for-sale		7,360
Loans held for sale	0	0
Other assets	0	0
Total assets	6,178	7,360
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
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	0
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	0
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	6,178
Available-for-sale		7,360
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	0
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	0
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Equity securities
Investment securities
Available-for-sale		0
Significant Unobservable Inputs (Level 3) \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	36,957	48,373
Loan servicing rights	373	5,350
Foreclosed assets	4,450	3,472
Total	41,780	57,195
Fair Value \| Recurring fair value measurements
Investment securities
Available for sale	1,749,001
Available-for-sale		1,493,905
Loans held for sale	31,675	15,119
Other assets	28,539	26,417
Total assets	1,809,215	1,535,441
Liabilities
Other liabilities	44,917	24,330
Total liabilities	44,917	24,330
Fair Value \| Recurring fair value measurements \| U.S. Treasury securities
Investment securities
Available for sale	48,363
Available-for-sale		49,642
Fair Value \| Recurring fair value measurements \| U.S. government agency securities
Investment securities
Available for sale	36,513
Available-for-sale		42,505
Fair Value \| Recurring fair value measurements \| Obligations of states and political subdivisions
Investment securities
Available for sale	205,237
Available-for-sale		112,884
Fair Value \| Recurring fair value measurements \| Residential mortgage-backed securities
Investment securities
Available for sale	1,412,849
Available-for-sale		1,223,295
Fair Value \| Recurring fair value measurements \| Trust preferred securities
Investment securities
Available for sale	1,590
Available-for-sale		3,214
Fair Value \| Recurring fair value measurements \| Corporate and other debt securities
Investment securities
Available for sale	44,449
Available-for-sale		51,164
Fair Value \| Recurring fair value measurements \| Equity securities
Investment securities
Available-for-sale		11,201
Fair Value \| Non-recurring fair value measurements
Non-recurring fair value measurements
Collateral dependent impaired loans	36,957	48,373
Loan servicing rights	373	5,350
Foreclosed assets	4,450	3,472
Total	$ 41,780	$ 57,195

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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of asset after deduction of liability.

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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 portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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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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