Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 41,168,000	$ 7,869,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred loan fees and costs, premiums and discounts	1,055,000	1,420,000
Net amortization of premiums and discounts on securities	787,000	1,017,000
Net amortization on mortgage servicing rights	(78,000)	57,000
Amortization of debt issuance costs	0	890,000
Depreciation and amortization of office properties and equipment	3,366,000	2,748,000
Provision for loan losses	1,705,000	5,900,000
Gain on securities transactions	(1,721,000)	(116,000)
Change in fair value of equity securities	(189,000)	0
Gain on sales of loans	(710,000)	(15,000)
Loss on real estate owned	1,000	45,000
Deferred tax (benefit) expense	(7,160,000)	6,764,000
Increase in accrued interest receivable	(529,000)	(2,679,000)
Increase in other assets	(44,037,000)	(13,801,000)
Increase in accrued expenses and other liabilities	36,367,000	3,505,000
Income on bank-owned life insurance	(4,449,000)	(3,435,000)
Contribution of common stock to Columbia Bank Foundation	0	34,767,000
Employee stock ownership plan expense	2,619,000	1,700,000
Stock based compensation	1,630,000	0
Increase in deferred compensation obligations under Rabbi Trust	(45,000)	0
Net cash provided by operating activities	29,780,000	46,636,000
Cash flows from investing activities:
Proceeds from sales of debt securities available for sale	31,811,000	0
Proceeds from sales of equity securities	926,000	0
Proceeds from paydowns/maturities/calls of debt securities available for sale	88,504,000	60,959,000
Proceeds from paydowns/maturities/calls on debt securities held to maturity	37,968,000	6,846,000
Purchases of debt securities available for sale	(143,196,000)	(361,263,000)
Purchases of debt securities held to maturity	(65,171,000)	(31,639,000)
Purchase of equity securities	(416,000)	0
Proceeds from sales of loans held-for-sale	94,834,000	0
Proceeds from sales of loans receivable	10,273,000	3,695,000
Purchases of loans receivable	(29,885,000)	(4,715,000)
Net increase in loans receivable	(297,434,000)	(451,223,000)
Purchase of bank-owned life insurance	0	(30,000,000)
Proceeds from bank-owned life insurance death benefit	1,015,000	811,000
Proceeds from redemptions of Federal Home Loan Bank stock	47,860,000	51,676,000
Purchases of Federal Home Loan Bank stock	(45,999,000)	(63,544,000)
Additions to office properties and equipment	(15,039,000)	(8,799,000)
Proceeds from sales of real estate owned	91,000	914,000
Net cash (used in) investing activities	(283,858,000)	(826,282,000)
Cash flows from financing activities:
Net increase in deposits	369,449,000	109,030,000
Proceeds from long-term borrowings	127,337,000	168,930,000
Payments on long-term borrowings	(220,000,000)	(170,000,000)
Net increase in short-term borrowings	32,600,000	258,400,000
Payments on trust preferred securities	0	(51,547,000)
Increase in advance payments by borrowers for taxes and insurance	2,513,000	7,169,000
Issuance of common stock	14,000	492,428,000
Purchase of treasury stock	(42,084,000)	0
Purchase of employee stock ownership plan shares	0	(45,428,000)
Net cash provided by financing activities	269,829,000	768,982,000
Net increase (decrease) in cash and cash equivalents	15,751,000	(10,664,000)
Cash and cash equivalents at beginning of year	42,201,000	65,498,000
Cash and cash equivalents at end of period	57,952,000	54,834,000
Cash paid during the period for:
Interest on deposits and borrowings	64,892,000	45,306,000
Income tax payments, net of (refunds)	(4,293,000)	13,435,000
Non-cash investing and financing activities:
Transfer of loans receivable to real estate owned	0	251,000
Transfer of loans receivable to loans held-for-sale	86,043,000	1,860,000
Securitization of loans	$ 21,615,000	$ 0