Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income (loss)	$ 26,950,000	$ (2,958,000)
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Amortization of deferred loan fees and costs, premiums and discounts	1,102,000	837,000
Net amortization of premiums and discounts on securities	589,000	707,000
Net amortization on mortgage servicing rights	(52,000)	40,000
Amortization of debt issuance costs	0	312,000
Depreciation and amortization of office properties and equipment	2,170,000	1,834,000
Provision for loan losses	548,000	4,400,000
Gain on securities transactions	(465,000)	(116,000)
Change in fair value of equity securities	(247,000)	0
Gain on sales of loans	(328,000)	(15,000)
Loss on real estate owned	1,000	13,000
Deferred tax (benefit) expense	(7,160,000)	6,811,000
Increase in accrued interest receivable	(1,416,000)	(1,152,000)
Increase in other assets	(34,322,000)	(17,474,000)
Increase in accrued expenses and other liabilities	12,880,000	3,166,000
Income on bank-owned life insurance	(2,665,000)	(2,127,000)
Contribution of common stock to Columbia Bank Foundation	0	34,767,000
Employee stock ownership plan expense	1,738,000	744,000
Increase in deferred compensation obligations under Rabbi Trust	(98,000)	0
Net cash (used in) provided by operating activities	(775,000)	29,789,000
Cash flows from investing activities:
Proceeds from sales of debt securities available for sale	15,711,000	0
Proceeds from sales of equity securities	765,000	0
Proceeds from paydowns/maturities/calls of debt securities available for sale	49,569,000	39,507,000
Proceeds from paydowns/maturities/calls on debt securities held to maturity	9,964,000	4,453,000
Purchases of debt securities available for sale	(80,499,000)	(278,610,000)
Purchases of debt securities held to maturity	(47,671,000)	(19,761,000)
Purchase of equity securities	(417,000)	0
Proceeds from sales of loans held-for-sale	45,003,000	0
Proceeds from sales of loans receivable	2,483,000	3,695,000
Purchases of loans receivable	(29,885,000)	(4,715,000)
Net increase in loans receivable	(168,486,000)	(252,786,000)
Death benefit proceeds from bank-owned life insurance	0	811,000
Proceeds from redemptions of Federal Home Loan Bank stock	32,851,000	40,226,000
Purchases of Federal Home Loan Bank stock	(32,526,000)	(40,571,000)
Additions to office properties and equipment	(11,387,000)	(5,837,000)
Proceeds from sales of real estate owned	91,000	286,000
Net cash (used in) investing activities	(214,434,000)	(513,302,000)
Cash flows from financing activities:
Net increase in deposits	254,772,000	31,517,000
Proceeds from long-term borrowings	78,991,000	154,050,000
Payments on long-term borrowings	(160,000,000)	(120,000,000)
Net increase (decrease) in short-term borrowings	55,100,000	(32,801,000)
Increase in advance payments by borrowers for taxes and insurance	2,389,000	5,432,000
Issuance of common stock	0	492,428,000
Purchase of treasury stock	(3,867,000)	0
Purchase of employee stock ownership plan shares	0	(45,428,000)
Net cash provided by financing activities	227,385,000	485,198,000
Net increase in cash and cash equivalents	12,176,000	1,685,000
Cash and cash equivalents at beginning of year	42,201,000	65,498,000
Cash and cash equivalents at end of period	54,377,000	67,183,000
Cash paid during the period for:
Interest on deposits and borrowings	21,491,000	26,947,000
Income tax payments, net of (refunds)	(5,174,000)	9,435,000
Non-cash investing and financing activities:
Transfer of loans receivable to loans held-for-sale	38,966,000	0
Securitization of loans	$ 21,615,000	$ 0