Parent-only Financial Information - Statement of Cash Flows (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income	$ 36,086,000	$ 86,173,000	$ 92,049,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	2,350,000	1,980,000	1,025,000
Gain on securities transactions	10,847,000	(210,000)	(2,025,000)
Change in fair value of equity securities	(695,000)	401,000	1,792,000
Loss on extinguishment of debt	300,000	0	2,851,000
Deferred tax (benefit) expense	3,375,000	12,769,000	17,709,000
(Increase) in other assets	(33,992,000)	(9,884,000)	(22,159,000)
Increase in accrued expenses and other liabilities	3,282,000	24,998,000	1,926,000
Net cash provided by operating activities	40,716,000	142,158,000	98,704,000
Cash flows from investing activities:
Proceeds from sales of equity securities	0	0	1,390,000
Proceeds from paydown/maturities/calls of debt securities available for sale	100,855,000	281,959,000	368,249,000
Purchases of equity securities	0	0	(91,000)
Net cash acquired in acquisitions	0	140,769,000	20,417,000
Net cash provided by (used in) investing activities	39,645,000	(614,725,000)	(443,605,000)
Cash flows from financing activities:
Repayment of term note	(30,300,000)	0	0
Proceeds from term note	0	0	29,841,000
Purchase of treasury stock	(80,497,000)	(93,996,000)	(107,774,000)
Exercise of stock options	(24,000)	(393,000)	(25,000)
Repurchase of shares for taxes	(623,000)	(4,614,000)	(357,000)
Net cash provided by (used in) financing activities	163,660,000	580,832,000	(7,093,000)
Net increase (decrease) in cash and cash equivalents	244,021,000	108,265,000	(351,994,000)
Cash and cash equivalents at beginning of year	179,228,000	70,963,000	422,957,000
Cash and cash equivalents at end of year	423,249,000	179,228,000	70,963,000
Non-cash investing and financing activities:
Excise tax on net stock repurchases	800,000	0	0
Acquisition:
Net cash and cash equivalents acquired in acquisition	0	140,769,000	20,417,000
Parent Company
Cash flows from operating activities:
Net income	36,086,000	86,173,000	92,049,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	74,000	73,000	21,000
Gain on securities transactions	0	0	(383,000)
Change in fair value of equity securities	10,000	15,000	35,000
Loss on extinguishment of debt	300,000	0	0
Deferred tax (benefit) expense	2,019,000	2,463,000	1,830,000
(Increase) in other assets	8,894,000	(642,000)	(7,721,000)
Increase in accrued expenses and other liabilities	(890,000)	(997,000)	691,000
Equity in undistributed (earnings)of subsidiaries	8,432,000	(9,132,000)	(27,652,000)
Net cash provided by operating activities	54,925,000	77,953,000	58,870,000
Cash flows from investing activities:
Proceeds from sales of equity securities	0	0	1,390,000
Purchases of equity securities	0	0	(91,000)
Repayment of loan receivable from Columbia Bank	1,755,000	1,675,000	1,599,000
Net cash acquired in acquisitions	0	31,000	0
Net cash provided by (used in) investing activities	1,755,000	1,706,000	2,898,000
Cash flows from financing activities:
Repayment of term note	(30,300,000)	0	0
Proceeds from term note	0	0	29,841,000
Purchase of treasury stock	(80,497,000)	(93,996,000)	(107,774,000)
Exercise of stock options	42,000	325,000	(25,000)
Issuance of common stock allocated to restricted stock award grants	4,066,000	2,624,000	0
Restricted stock forfeitures	(501,000)	(1,451,000)	(1,234,000)
Repurchase of shares for taxes	(623,000)	(4,614,000)	(357,000)
Issuance of treasury stock allocated to restricted stock award grants	0	0	896,000
Net cash provided by (used in) financing activities	(107,813,000)	(97,112,000)	(78,653,000)
Net increase (decrease) in cash and cash equivalents	(51,133,000)	(17,453,000)	(16,885,000)
Cash and cash equivalents at beginning of year	59,885,000	77,338,000	94,223,000
Cash and cash equivalents at end of year	8,752,000	59,885,000	77,338,000
Non-cash investing and financing activities:
Excise tax on net stock repurchases	800,000	0	0
Acquisition:
Net cash and cash equivalents acquired in acquisition	$ 0	$ 31,000	$ 0