Long-Term Debt (Narrative) (Details) (USD $)	9 Months Ended							9 Months Ended				9 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Senior Notes Due 2015 [Member]	Sep. 30, 2014 Senior Notes Due 2016 [Member]	Sep. 30, 2014 Combined Credit Agreements [Member]	Dec. 31, 2013 Combined Credit Agreements [Member]	Sep. 30, 2014 Canadian Credit Facility [Member]	Sep. 30, 2014 Combined Credit Agreements [Member]	Sep. 30, 2014 Maximum [Member] U.S. Credit Facility [Member]	Sep. 30, 2014 Maximum [Member] Combined Credit Agreements [Member]	Sep. 30, 2014 Maximum [Member] Global Letter Of Credit [Member]	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Multiple Subsidiaries Set Two [Member] U.S. Credit Facility [Member]	Sep. 30, 2014 London Interbank Offered Rate (LIBOR) [Member] U.S. Credit Facility [Member]	Sep. 30, 2014 Libor [Member] Maximum [Member] Canadian Credit Facility [Member]	Sep. 30, 2014 Libor [Member] Minimum [Member] Canadian Credit Facility [Member]	Sep. 30, 2014 2013 [Member] Senior Notes [Member] Senior Notes Due 2015 [Member]	Sep. 30, 2014 2013 [Member] Senior Notes [Member] Senior Notes Due 2016 [Member]	Sep. 30, 2014 Subsequent Event [Member] Combined Credit Agreements [Member]
Debt Instrument [Line Items]
Percentage of ownership interest							100.00%						65.00%
Borrowing capacity					$ 325,000,000						$ 280,000,000
Line of Credit Facility, Maximum Borrowing Capacity					650,000,000	1,750,000,000													450,000,000
Redemption percentage of par value																	101.938%	105.875%
Available borrowing under combined credit agreements								6,700,000
Commitment fee percentage								0.50%	1.75%	0.50%
EBITDA to interest expense												2.25
Repayments of Long-term Debt	193,689,000	1,308,382,000	10,900,000	8,900,000
Issuance of debt	$ 243,184,000	$ 1,173,306,000
Debt Instrument, Basis Spread on Variable Rate									2.75%					1.00%	3.75%	2.75%