Fair Value Measurements - Carrying Amounts and Estimated Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair values of defined benefit pension plan assets by category of the firm
Securities available for sale, at fair value	$ 1,250,777	$ 671,488
Loans held for sale	411,427	108,316
Mortgage servicing rights	48,230	39,339	$ 26,302
Quoted Prices In Active Markets for Identical Assets (Level 1)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	569,111	281,453
Securities available for sale, at fair value	0	0
Loans held for sale	0	0
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	0	0
Financial liabilities
Deposits	7,765,773	6,114,391
Short-term borrowings	387,706	89,814
Other long-term borrowings	53	98
Federal Home Loan Bank advances	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Significant Other Observable Inputs (Level 2)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	0	0
Securities available for sale, at fair value	1,240,144	662,100
Loans held for sale	219,848	108,316
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	6,519	5,977
Financial liabilities
Deposits	2,337,334	1,809,085
Short-term borrowings	0	0
Other long-term borrowings	0	0
Federal Home Loan Bank advances	6,751	7,661
Junior subordinated debentures	109,766	69,702
Subordinated notes	148,875	118,650
Derivative instruments	8,388	6,039
Significant Unobservable Inputs (Level 3)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	0	0
Securities available for sale, at fair value	10,633	9,388
Loans held for sale	191,579	0
Loans, net	8,818,039	7,514,185
Mortgage servicing rights	61,111	47,868
Derivative instruments	0	0
Financial liabilities
Deposits	0	0
Short-term borrowings	0	0
Other long-term borrowings	0	0
Federal Home Loan Bank advances	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Carrying Value
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	569,111	281,453
Securities available for sale, at fair value	1,250,777	671,488
Loans held for sale	411,427	108,316
Loans, net	9,034,103	7,574,111
Mortgage servicing rights	48,230	39,339
Derivative instruments	6,519	5,977
Financial liabilities
Deposits	10,128,557	7,921,075
Short-term borrowings	387,706	89,814
Other long-term borrowings	53	98
Federal Home Loan Bank advances	6,690	7,493
Junior subordinated debentures	109,636	85,881
Subordinated notes	147,239	114,074
Derivative instruments	8,388	6,039
Fair Value
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	569,111	281,453
Securities available for sale, at fair value	1,250,777	671,488
Loans held for sale	411,427	108,316
Loans, net	8,818,039	7,514,185
Mortgage servicing rights	61,111	47,868
Derivative instruments	6,519	5,977
Financial liabilities
Deposits	10,103,107	7,923,476
Short-term borrowings	387,706	89,814
Other long-term borrowings	53	98
Federal Home Loan Bank advances	6,751	7,661
Junior subordinated debentures	109,766	69,702
Subordinated notes	148,875	118,650
Derivative instruments	$ 8,388	$ 6,039

Junior Subordinated Debt Obligations, Fair Value Disclosure

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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 portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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