Fair Value Measurements - Summary of Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 2,062,813	$ 837,493	$ 1,253,573	$ 1,020,396
Securities available for sale	2,799,941	2,437,296
Securities held to maturity	1,221	1,446
Other securities	251,161	222,161
Loans held for sale	625,984	387,514
Net loans	17,992,402	13,712,129
Mortgage servicing rights	20,200	0
Deposits	19,893,843	13,852,421
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,062,813	837,493
Securities available for sale	2,799,941	2,437,296
Securities held to maturity	1,221	1,446
Other securities	251,161	222,161
Loans held for sale	625,984	387,514
Net loans	17,777,281	13,635,072
Derivative financial assets	29,578	4,527
Mortgage servicing rights	20,200
Deposits	19,893,843	13,852,421
Short-term borrowings	176,168	374,654
Long-term borrowings	1,633,891	1,838,029
Derivative financial liabilities	14,307	3,065
Carrying Amount [Member] \| Marketable Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	9,875	8,894
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,062,813	837,493
Securities available for sale	2,799,941	2,437,296
Securities held to maturity	1,220	1,447
Other securities	238,603	211,053
Loans held for sale	625,984	387,514
Net loans	17,191,993	13,185,955
Derivative financial assets	29,578	4,527
Mortgage servicing rights	20,200
Deposits	19,902,498	13,843,077
Short-term borrowings	176,168	374,654
Long-term borrowings	1,597,685	1,820,297
Derivative financial liabilities	14,307	3,065
Fair Value [Member] \| Marketable Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	9,875	8,894
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Securities available for sale	6,432	6,586
Securities held to maturity	0	0
Other securities	0	0
Loans held for sale	0	0
Net loans	0	0
Derivative financial assets	0	0
Mortgage servicing rights	0
Deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Derivative financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Marketable Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	9,875	8,894
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,062,813	837,493
Securities available for sale	2,780,672	2,426,007
Securities held to maturity	200	427
Other securities	0	0
Loans held for sale	60,187	3,139
Net loans	0	0
Derivative financial assets	9,158	9
Mortgage servicing rights	0
Deposits	19,902,498	13,843,077
Short-term borrowings	176,168	374,654
Long-term borrowings	1,597,685	1,820,297
Derivative financial liabilities	14,307	3,065
Significant Other Observable Inputs (Level 2) [Member] \| Marketable Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Securities available for sale	12,837	4,703
Securities held to maturity	1,020	1,020
Other securities	238,603	211,053
Loans held for sale	565,797	384,375
Net loans	17,191,993	13,185,955
Derivative financial assets	20,420	4,518
Mortgage servicing rights	20,200
Deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Derivative financial liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Marketable Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	$ 0	$ 0

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

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The sum of cash and cash equivalents plus Federal Funds Sold. Cash and cash equivalents consist of short term, highly liquid investments that are readily convertible to known amounts of cash and are so near their maturity that they present negligible risk of changes in value due to changes in interest rates -- usually with an original maturity less than 90 days.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount before allowance and after 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.

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Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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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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Amount of investments classified as other.

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