Employee Benefit Plans and Postretirement Benefits: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	4.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	5.00%
Company's 401(k) Employer Match Expense	$ 5.6	$ 7.2
Annual matching contribution to defined contribution plan, Common Stock	2.7
Defined Contribution Plan, Contributions by Employer, Common Stock, Value	21.6
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	0.8
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments	0	9.5
Postretirement Benefit Contributions	0.5
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	1.8
Accumulated Other Comprehensive Income | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments		9.5
Cost of services | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments		5.1
Selling, general and administrative | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments		$ 4.4