Treasury Stock: (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) shares
Treasury stock purchase plan [Abstract]
Treasury Stock Purchase Plan	$ 40.0
Treasury Stock Purchase Plan Remaining Available	$ 22.5
Shares Paid for Tax Withholding for Share Based Compensation | shares	17,299
Payments Related to Tax Withholding for Share-based Compensation	$ 1.5