Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Securities available for sale	$ 1,247,333	$ 721,369
State tax credits held for sale	0	0
Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	1,247,333	721,369
State tax credits held for sale	46,981	39,169
Derivatives	13,561	3,023
Liabilities
Derivatives	18,451	3,023
Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	10,033	98,498
Obligations of states and political subdivisions
Assets
Securities available for sale	170,313	26,810
Agency mortgage-backed securities
Assets
Securities available for sale	934,111	586,136
US Treasury Bill Securities [Member]
Assets
Securities available for sale	10,247	9,925
Corporate Debt Securities [Member]
Assets
Securities available for sale	122,629
Recurring basis \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	1,247,333	721,369
Other investments	164	121
Derivatives	13,561	3,023
Total assets	1,261,058	724,513
Liabilities
Derivatives		3,023
Total liabilities	18,451	3,023
Recurring basis \| Obligations of U.S. Government-sponsored enterprises \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	10,033	98,498
Recurring basis \| Obligations of states and political subdivisions \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	170,313	26,810
Recurring basis \| Agency mortgage-backed securities \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	934,111	586,136
Recurring basis \| US Treasury Bill Securities [Member] \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	10,247	9,925
Recurring basis \| Corporate Debt Securities [Member] \| Estimate of Fair Value Measurement [Member]
Assets
Securities available for sale	122,629
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale	0	0
Other investments	164	121
Derivatives	0	0
Total assets	164	121
Liabilities
Derivatives	0	0
Total liabilities	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of states and political subdivisions
Assets
Securities available for sale	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Agency mortgage-backed securities
Assets
Securities available for sale	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| US Treasury Bill Securities [Member]
Assets
Securities available for sale	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Corporate Debt Securities [Member]
Assets
Securities available for sale	0
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets
Securities available for sale	1,247,333	721,369
Other investments	0	0
Derivatives	13,561	3,023
Total assets	1,260,894	724,392
Liabilities
Derivatives	18,451	3,023
Total liabilities	18,451	3,023
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	10,033	98,498
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of states and political subdivisions
Assets
Securities available for sale	170,313	26,810
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Agency mortgage-backed securities
Assets
Securities available for sale	934,111	586,136
Recurring basis \| Significant Other Observable Inputs (Level 2) \| US Treasury Bill Securities [Member]
Assets
Securities available for sale	10,247	9,925
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Corporate Debt Securities [Member]
Assets
Securities available for sale	122,629
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets
Securities available for sale	0	0
Other investments	0	0
Derivatives	0	0
Total assets	0	0
Liabilities
Derivatives	0	0
Total liabilities	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of states and political subdivisions
Assets
Securities available for sale	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Agency mortgage-backed securities
Assets
Securities available for sale	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| US Treasury Bill Securities [Member]
Assets
Securities available for sale	$ 0	$ 0

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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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Fair value of financial and nonfinancial obligations.

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