Financing Arrangements Revolving Credit Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Cash Institution Covenant	$ 200,000
Line of Credit Facility, Maximum Borrowing Capacity	250,000
Unrestricted Cash Covenant	400,000
Letters of Credit Outstanding, Amount	11,600	$ 11,600
Previous Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	250,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 45,000
Minimum [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate Description	0.005
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Maximum [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate Description	0.0225
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.40%
Geographic Distribution, Domestic [Member]
Line of Credit Facility [Line Items]
Securities Owned and Pledged as Collateral, Description	1
Geographic Distribution, Foreign [Member]
Line of Credit Facility [Line Items]
Securities Owned and Pledged as Collateral, Description	0.65