Investment securities - Summary of Amortized Cost and Fair Value of Securities (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Abstract]
Amortized cost	$ 1,673,798,000	$ 1,137,848,000
Gross unrealized gains	23,120,000	35,376,000
Gross unrealized losses	(18,393,000)	(824,000)
Allowance for credit losses for investments	0	0
Fair Value	1,678,525,000	1,172,400,000
U.S. government agency securities
Debt Securities, Available-for-sale [Abstract]
Amortized cost	34,023,000	2,000,000
Gross unrealized gains	18,000	3,000
Gross unrealized losses	(171,000)	0
Allowance for credit losses for investments	0	0
Fair Value	33,870,000	2,003,000
Mortgage-backed securities - residential
Debt Securities, Available-for-sale [Abstract]
Amortized cost	1,281,285,000	760,099,000
Gross unrealized gains	6,072,000	14,040,000
Gross unrealized losses	(17,985,000)	(803,000)
Allowance for credit losses for investments	0	0
Fair Value	1,269,372,000	773,336,000
Mortgage-backed securities - commercial
Debt Securities, Available-for-sale [Abstract]
Amortized cost	15,024,000	20,226,000
Gross unrealized gains	272,000	1,362,000
Gross unrealized losses	(46,000)	0
Allowance for credit losses for investments	0	0
Fair Value	15,250,000	21,588,000
Municipal securities
Debt Securities, Available-for-sale [Abstract]
Amortized cost	322,052,000	336,543,000
Gross unrealized gains	16,718,000	19,806,000
Gross unrealized losses	(160,000)	(20,000)
Allowance for credit losses for investments	0	0
Fair Value	338,610,000	356,329,000
U.S. Treasury securities
Debt Securities, Available-for-sale [Abstract]
Amortized cost	14,914,000	16,480,000
Gross unrealized gains	0	148,000
Gross unrealized losses	(6,000)	0
Allowance for credit losses for investments	0	0
Fair Value	14,908,000	16,628,000
Corporate securities
Debt Securities, Available-for-sale [Abstract]
Amortized cost	6,500,000	2,500,000
Gross unrealized gains	40,000	17,000
Gross unrealized losses	(25,000)	(1,000)
Allowance for credit losses for investments	0	0
Fair Value	$ 6,515,000	$ 2,516,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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-Name Accounting Standards Codification
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Amount excluding accrued interest, of allowance for credit loss on 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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-Publisher FASB
-Name Accounting Standards Codification
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