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RETIREMENT PLANS: (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Retirement Benefits [Abstract] |  |  |
Service cost - benefits earned | $ 1,218 | $ 1,388 | $ 1,432
Interest cost on projected benefit obligation | 3,465 | 3,194 | 3,621
Expected return on plan assets | (3,585) | (3,962) | (3,940)
Net amortization and deferral | 1,558 | 1,448 | 1,205
Net periodic pension cost | 2,656 | 2,068 | 2,318
Net loss (gain) during the period | 6,362 | (1,192) | 5,366
Amortization of prior service cost | 1 | 1 | 1
Amortization of unrecognized gain (loss) | (1,558) | (1,447) | (1,204)
Total recognized in other comprehensive (income) loss | (4,803) | 2,640 | (4,161)
Total recognized net periodic pension cost and other comprehensive income | $ 7,459 | $ (572) | $ 6,479

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