Debt and Financing Arrangements (Financing Structure) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Components of financing structure:
Outstanding, total	$ 1,594,017	[1]	$ 1,816,445	[1]
Balance, debt	798,499	[2]	798,215	[2]
7.5% Senior notes due 2016 [Member]
Components of financing structure:
Outstanding, debt	500,000	[1]	500,000	[1]
Balance, debt	499,512	[2]	499,347	[2]
5.5% Senior notes due 2020 [Member]
Components of financing structure:
Outstanding, debt	300,000	[1]	300,000	[1]
Balance, debt	298,987	[2]	298,868	[2]
$1,000,000 secured letter of credit facility - uncommitted [Member]
Components of financing structure:
Outstanding, credit facility	707,915	[1]	907,592	[1]
Credit facility, maximum borrowing capacity	1,000,000		1,000,000
$450,000 secured letter of credit facility [Member]
Components of financing structure:
Outstanding, credit facility	86,102	[1]	108,853	[1]
Credit facility, maximum borrowing capacity	$ 450,000		$ 450,000

[1] Indicates utilization of commitment amount, not drawn borrowings.

[2] Represents the principal amount borrowed, net of unamortized discount.