Parent company financial statements - Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net income	$ 190,285	$ 63,621	$ 83,814
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Loss on other assets	(323)	90	104
Stock-based compensation expense	10,282	10,214	7,089
Net cash provided by (used in) operating activities	54,878	(270,002)	63,905
Investing Activities
Net cash (used in) provided by investing activities	(849,558)	310,136	(182,913)
Financing Activities
Payment of dividends	(21,583)	(14,264)	(10,045)
Payments on subordinated debt	(60,000)	0	0
Net proceeds from sale of common stock under employee stock purchase program	1,480	978	804
Repurchase of common stock	(7,595)	0	0
Net cash provided by financing activities	1,274,522	1,045,083	226,333
Net change in cash and cash equivalents	479,842	1,085,217	107,325
Cash and cash equivalents at beginning of the period	1,317,898	232,681	125,356
Cash and cash equivalents at end of the period	1,797,740	1,317,898	232,681
Supplemental cash flow information:
Dividends declared not paid on restricted stock units	400	238	149
Parent Company
Operating Activities
Net income	190,285	63,621	83,814
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity in undistributed income of bank subsidiary	(68,351)	(15,168)	(85,750)
Equity in undistributed income of nonbank subsidiary	635	(506)	0
Gain on investments	(249)	(217)	0
Loss on other assets	0	0	16
Stock-based compensation expense	10,282	10,214	7,089
(Increase) decrease in other assets	(3,916)	(9,717)	1,056
Decrease in other liabilities	(10,836)	(13,363)	(9,711)
Net cash provided by (used in) operating activities	117,850	34,864	(3,486)
Investing Activities
Net cash paid in business combinations (See Note 2)	0	(35,505)	0
Proceeds from sale of equity securities	1,422	0	0
Net cash (used in) provided by investing activities	1,422	(35,505)	0
Financing Activities
Accretion of interest rate premium on subordinated debt	(369)	(436)	0
Payment of dividends	(21,583)	(14,264)	(10,045)
Payments on subordinated debt	(60,000)	0	0
Payments on other borrowings	(15,000)	0	0
Proceeds from other borrowings	0	15,000	0
Net proceeds from sale of common stock under employee stock purchase program	1,480	978	804
Repurchase of common stock	(7,595)	0	0
Net cash provided by financing activities	(103,067)	1,278	(9,241)
Net change in cash and cash equivalents	16,205	637	(12,727)
Cash and cash equivalents at beginning of the period	5,310	4,673	17,400
Cash and cash equivalents at end of the period	21,515	5,310	4,673
Supplemental cash flow information:
Dividends declared not paid on restricted stock units	400	238	149
Noncash dividend from bank subsidiary	0	956	0
Noncash security distribution to bank subsidiary	$ 2,646	$ 0	$ 0