Stock Plans: (Assumptions Used for Performance Share Units) (Details) - Performance Shares	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average risk-free interest rate	4.10%	4.20%	4.10%
Average expected volatility	21.00%	19.90%	24.30%