Long-Term Debt (Revolving Credit Facility) (Details) (Line of Credit, USD $)	3 Months Ended
Mar. 31, 2015
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 400,000,000
Revolving credit facility, amount outstanding	0us-gaap_LineOfCredit
Percentage of commitment on borrowing availability	0.25%
Letters of credit outstanding	29,959,000
Remaining borrowing capacity	370,041,000
LIBOR [Member]
Line of Credit Facility [Line Items]
Maximum basis spread, provided company is rated investment grade	1.50%
Minimum
Line of Credit Facility [Line Items]
Increase in credit facility borrowings	25,000,000
Minimum \| LIBOR [Member]
Line of Credit Facility [Line Items]
Percentage added to basis to find interest rate	1.25%
Minimum \| Base Rate [Member]
Line of Credit Facility [Line Items]
Percentage added to basis to find interest rate	0.00%
Maximum
Line of Credit Facility [Line Items]
Increase in credit facility borrowings	$ 200,000,000
Maximum \| LIBOR [Member]
Line of Credit Facility [Line Items]
Percentage added to basis to find interest rate	1.75%
Maximum \| Base Rate [Member]
Line of Credit Facility [Line Items]
Percentage added to basis to find interest rate	0.50%

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References+ Details