Parent-only Financial Information - Statement of Cash Flows (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 92,049,000	$ 57,603,000	$ 54,717,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	1,025,000	1,048,000	222,000
Gain on securities transactions	(2,025,000)	(370,000)	(2,612,000)
Change in fair value of equity securities	1,792,000	(767,000)	(305,000)
Deferred tax expense	17,709,000	9,738,000	7,527,000
(Increase) in other assets	(22,159,000)	(75,127,000)	(51,856,000)
(Decrease) increase in accrued expenses and other liabilities	1,926,000	32,891,000	3,032,000
Net cash provided by operating activities	98,704,000	49,044,000	21,824,000
Cash flows from investing activities:
Proceeds from sales of equity securities	1,390,000	0	1,065,000
Proceeds from paydown/maturities/calls of debt securities available for sale	368,249,000	247,908,000	149,683,000
Purchases of equity securities	(91,000)	0	(416,000)
Repayment of loan receivable from Columbia Bank	0	35,613,000	11,671,000
Net cash acquired in acquisitions	20,417,000	155,248,000	(31,288,000)
Net cash (used in) provided by investing activities	(443,605,000)	257,645,000	(521,014,000)
Cash flows from financing activities:
Payments of subordinated debt and trust preferred securities	0	(16,600,000)	0
Proceeds from term note	29,841,000	0	0
Purchase of treasury stock	(107,774,000)	(108,166,000)	(55,309,000)
Exercise of options	(25,000)	0	0
Restricted stock forfeitures	0	(24,000)	(736,000)
Repurchase of shares for taxes	(357,000)	(174,000)	0
Issuance of treasury stock allocated to restricted stock award grants	0	0	1,095,000
Net cash (used in) provided by financing activities	(7,093,000)	40,721,000	532,536,000
Net (decrease) increase in cash and cash equivalents	(351,994,000)	347,410,000	33,346,000
Cash and cash equivalents at beginning of year	422,957,000	75,547,000	42,201,000
Cash and cash equivalents at end of year	70,963,000	422,957,000	75,547,000
Non-cash assets acquired:
Equity securities	0	1,796,000	1,073,000
Other assets	616,000	7,964,000	4,301,000
Total non-cash assets acquired	296,081,000	271,958,000	856,640,000
Liabilities assumed:
Borrowings	59,908,000	37,728,000	82,761,000
Total liabilities assumed	275,342,000	377,344,000	880,399,000
Net non-cash assets acquired (liabilities assumed)	20,739,000	(105,386,000)	(23,759,000)
Net cash and cash equivalents acquired in acquisitions	20,417,000	155,248,000	105,006,000
Parent Company
Cash flows from operating activities:
Net income	92,049,000	57,603,000	54,717,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	21,000	(278,000)	(71,000)
Gain on securities transactions	(383,000)	(2,000)	(236,000)
Change in fair value of equity securities	35,000	115,000	(65,000)
Deferred tax expense	1,830,000	1,411,000	1,453,000
(Increase) in other assets	(7,721,000)	(2,675,000)	(2,026,000)
(Decrease) increase in accrued expenses and other liabilities	691,000	(647,000)	3,515,000
Equity in undistributed (earnings) loss of subsidiaries	(27,652,000)	(8,027,000)	123,142,000
Net cash provided by operating activities	58,870,000	47,500,000	180,429,000
Cash flows from investing activities:
Proceeds from sales of equity securities	1,390,000	0	1,065,000
Proceeds from paydown/maturities/calls of debt securities available for sale	0	1,498,000	500,000
Purchases of equity securities	(91,000)	0	(416,000)
Repayment of loan receivable from Columbia Bank	1,599,000	1,521,000	1,457,000
Net cash acquired in acquisitions	0	0	(135,410,000)
Net cash (used in) provided by investing activities	2,898,000	3,019,000	(132,804,000)
Cash flows from financing activities:
Payments of subordinated debt and trust preferred securities	0	(16,600,000)	0
Proceeds from term note	29,841,000	0	0
Purchase of treasury stock	(107,774,000)	(108,166,000)	(55,309,000)
Exercise of options	(25,000)	0	0
Issuance of common stock allocated to restricted stock award grants	0	0	21,687,000
Restricted stock forfeitures	(1,234,000)	(199,000)	(736,000)
Repurchase of shares for taxes	(357,000)	(181,000)	0
Issuance of treasury stock allocated to restricted stock award grants	896,000	481,000	1,269,000
Net cash (used in) provided by financing activities	(78,653,000)	(124,665,000)	(33,089,000)
Net (decrease) increase in cash and cash equivalents	(16,885,000)	(74,146,000)	14,536,000
Cash and cash equivalents at beginning of year	94,223,000	168,369,000	153,833,000
Cash and cash equivalents at end of year	77,338,000	94,223,000	168,369,000
Non-cash assets acquired:
Debt securities available for sale	0	0	1,998,000
Equity securities	0	0	208,000
Other assets	0	0	1,492,000
Total non-cash assets acquired	0	0	3,698,000
Liabilities assumed:
Borrowings	0	0	23,901,000
Total liabilities assumed	0	0	23,901,000
Net non-cash assets acquired (liabilities assumed)	0	0	(20,203,000)
Net cash and cash equivalents acquired in acquisitions	$ 0	$ 0	$ 884,000