Fair Value Measurement - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 1,509,211		$ 1,186,292
Servicing assets, at fair value	21,267	$ 18,351	19,471	$ 19,939	$ 19,760	$ 19,693
Derivative assets	19,133		7,960
Derivative liabilities	20,327		8,519
Equity and other securities, at fair value	8,335		8,031
U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	25,951		41,830
U.S. Government Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	104,710		164,950
Obligations of States, Municipalities, and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	108,312		94,832
Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	57,208		49,330
Asset-Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	49,522		44,317
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Servicing assets, at fair value	21,267		19,471
Derivative assets	19,133		7,960
Derivative liabilities	20,327		8,519
Fair Value, Measurements, Recurring | Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	2,992
Equity and other securities, at fair value			2,952
Fair Value, Measurements, Recurring | Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	5,343
Equity and other securities, at fair value			5,079
Fair Value, Measurements, Recurring | U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	25,951		41,830
Fair Value, Measurements, Recurring | U.S. Government Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	104,710		164,950
Fair Value, Measurements, Recurring | Obligations of States, Municipalities, and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	108,312		94,832
Fair Value, Measurements, Recurring | Mortgage-Backed Securities; Residential | Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	824,037		490,236
Fair Value, Measurements, Recurring | Mortgage-Backed Securities; Residential | Non-Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	64,096		109,822
Fair Value, Measurements, Recurring | Mortgage-Backed Securities; Commercial | Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	263,732		159,701
Fair Value, Measurements, Recurring | Mortgage-Backed Securities; Commercial | Non-Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	11,643		31,274
Fair Value, Measurements, Recurring | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	57,208		49,330
Fair Value, Measurements, Recurring | Asset-Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	49,522		44,317
Fair Value, Measurements, Recurring | Level 1 | Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	2,992
Equity and other securities, at fair value			2,952
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	25,951		41,830
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	19,133		7,960
Derivative liabilities	20,327		8,519
Fair Value, Measurements, Recurring | Level 2 | Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	4,659
Equity and other securities, at fair value			4,379
Fair Value, Measurements, Recurring | Level 2 | U.S. Government Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	104,710		164,950
Fair Value, Measurements, Recurring | Level 2 | Obligations of States, Municipalities, and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	108,312		94,832
Fair Value, Measurements, Recurring | Level 2 | Mortgage-Backed Securities; Residential | Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	824,037		490,236
Fair Value, Measurements, Recurring | Level 2 | Mortgage-Backed Securities; Residential | Non-Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	64,096		109,822
Fair Value, Measurements, Recurring | Level 2 | Mortgage-Backed Securities; Commercial | Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	263,732		159,701
Fair Value, Measurements, Recurring | Level 2 | Mortgage-Backed Securities; Commercial | Non-Agency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	11,643		31,274
Fair Value, Measurements, Recurring | Level 2 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	57,208		49,330
Fair Value, Measurements, Recurring | Level 2 | Asset-Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	49,522		44,317
Fair Value, Measurements, Recurring | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Servicing assets, at fair value	21,267		19,471
Fair Value, Measurements, Recurring | Level 3 | Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 684
Equity and other securities, at fair value			$ 700