Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 36,949,000	$ 41,168,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred loan costs, fees and purchased premiums and discounts	818,000	1,055,000
Net amortization of premiums and discounts on securities	1,573,000	787,000
Net amortization of mortgage servicing rights	85,000	(78,000)
Amortization of intangible assets	783,000	0
Depreciation and amortization of office properties and equipment	4,947,000	3,366,000
Amortization of operating lease right-of-use assets	2,641,000	0
Provision for loan losses	17,820,000	1,705,000
Gain on securities transactions	(370,000)	(1,721,000)
Change in fair value of equity securities	(55,000)	(189,000)
Gain on securitizations	(1,523,000)	0
Gain on sale of loans	(1,899,000)	(710,000)
Loss on real estate owned	0	1,000
Loss on disposal of office properties and equipment	691,000	0
Loss on write-down of mortgage servicing rights	75,000	0
Deferred tax expense (benefit)	(3,864,000)	(7,160,000)
(Increase) in accrued interest receivable	(8,481,000)	(529,000)
(Increase) in other assets	(80,110,000)	(44,037,000)
Increase in accrued expenses and other liabilities	33,687,000	36,367,000
Income on bank-owned life insurance	(4,467,000)	(4,449,000)
Employee stock ownership plan expense	2,374,000	2,619,000
Stock based compensation	6,585,000	1,630,000
Increase in deferred compensation obligations under Rabbi Trust	(129,000)	(45,000)
Net cash provided by operating activities	8,130,000	29,780,000
Cash flows from investing activities:
Proceeds from sales of debt securities available for sale	20,761,000	31,811,000
Proceeds from sales of equity securities	0	926,000
Proceeds from paydowns/maturities/calls of debt securities available for sale	162,161,000	88,504,000
Proceeds from paydowns/maturities/calls of debt securities held to maturity	30,988,000	37,968,000
Purchases of debt securities available for sale	(201,504,000)	(143,196,000)
Purchases of debt securities held to maturity	(5,000,000)	(65,171,000)
Purchases of equity securities	0	(416,000)
Proceeds from sales of loans held-for-sale	111,764,000	94,834,000
Proceeds from sales of loans receivable	28,923,000	10,273,000
Purchases of loans receivable	0	(29,885,000)
Net increase in loans receivable	(294,040,000)	(297,434,000)
Proceeds from bank-owned life insurance death benefit	0	1,015,000
Proceeds from redemptions of Federal Home Loan Bank stock	40,717,000	47,860,000
Purchases of Federal Home Loan Bank stock	(22,544,000)	(45,999,000)
Additions to office properties and equipment	(3,750,000)	(15,039,000)
Proceeds from sale of real estate owned	0	91,000
Net cash acquired in acquisition	155,248,000	0
Net cash provided by (used in) investing activities	23,724,000	(283,858,000)
Cash flows from financing activities:
Net increase in deposits	650,572,000	369,449,000
Proceeds from long-term borrowings	90,000,000	127,337,000
Payments on long-term borrowings	(181,345,000)	(220,000,000)
Net (decrease) increase in short-term borrowings	(321,595,000)	32,600,000
Payment of subordinated debt	(16,600,000)	0
Increase in advance payments by borrowers for taxes and insurance	(2,235,000)	2,513,000
Issuance of common stock	0	14,000
Purchase of treasury stock	(60,286,000)	(42,084,000)
Purchase of employee stock ownership plan shares	0	0
Restricted stock forfeitures	(16,000)	0
Issuance of treasury stock allocated to restricted stock award grants	0	0
Net cash provided by financing activities	158,495,000	269,829,000
Net increase in cash and cash equivalents	190,349,000	15,751,000
Cash and cash equivalents at beginning of year	75,547,000	42,201,000
Cash and cash equivalents at end of period	265,896,000	57,952,000
Cash paid during the period for:
Interest on deposits and borrowings	60,772,000	64,892,000
Income tax payments, net of (refunds)	12,249,000	(4,293,000)
Non-cash investing and financing activities:
Transfer of loans receivable to loans held-for-sale	114,171,000	86,043,000
Securitization of loans	48,526,000	21,615,000
Initial recognition of operating lease right-of-use assets	22,218,000	0
Initial recognition of operating lease liabilities	23,290,000	0
Non-cash assets acquired:
Debt securities available for sale	51,479,000	0
Debt securities held to maturity	13,418,000	0
Equity securities	1,796,000	0
Federal Home Loan Bank stock	2,010,000	0
Loans receivable	171,593,000	0
Accrued interest receivable	679,000	0
Office properties and equipment, net	5,774,000	0
Bank-owned life insurance	17,245,000	0
Other assets	2,823,000	0
Total non-cash assets acquired	266,817,000	0
Liabilities assumed:
Deposits	333,234,000	0
Borrowings	37,728,000	0
Advance payments by borrowers for taxes and insurance	982,000	0
Accrued expenses and other liabilities	5,400,000	0
Total liabilities assumed	377,344,000	0
Net non-cash liabilities acquired	(110,527,000)	0
Net cash and cash equivalents acquired in acquisition	$ 155,248,000	$ 0