Long-Term Debt And Other Long-Term Liabilities (Narrative) (Details) (USD $)	0 Months Ended		9 Months Ended
	Jul. 24, 2012	May 18, 2011	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Credit facility maximum credit amount			$ 900,000,000	$ 750,000,000
Outstanding borrowing capacity used as a threshold to determine commitment fee, percent			1.00%
Origination, agency and syndication and other related fees			1,500,000
Payable assessment term for LIBOR			90 days
LIBOR interest rate plus one percent			LIBOR plus 1.00%
Outstanding Borrowings Subject To LIBOR			0
Outstanding borrowings					50,000,000
Current ratio of credit facility			1 to 1
Leverage ratio of long-term debt			4 to 1
Aggregate principal amount	650,000,000
Debt instrument issued at discount, percent of par	98.75%
Deducting fees for debt issuance	8,700,000	6,000,000
Repayment of outstanding borrowings under unsecured credit facility		220,300,000
Percentage of maximum, aggregate principal equity amount			35.00%
Proceed from equity offerings redemption price percentage			106.625%
Minimum redemption percentage of debt outstanding			65.00%
Equal redemption price percentage of principal amount of debt			100.00%
Senior notes repurchase price in percentage			101.00%
2012			11,400,000
2013			23,000,000
2014			8,400,000
2015			4,500,000
2016			3,500,000
Minimum [Member]
Debt Instrument [Line Items]
Commitment fee percentage under credit facility			0.375%
LIBOR plus interest rate			1.75%
Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage under credit facility			0.50%
LIBOR plus interest rate			2.50%
Maximum payment of dividends as a percentage of consolidated net income, prohibited under credit agreement			30.00%
Senior Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility maturity date			September 13, 2016
6.625% Senior Subordinated Notes Due 2021 [Member]
Debt Instrument [Line Items]
Aggregate principal amount	400,000,000	250,000,000
Interest percentage of senior subordinated notes		6.625%	6.625%
Debt instrument maturity date			May 15, 2021
Proceeds from sale of notes		244,000,000
Line Of Credit Facility Lender Determined Amount [Member]
Debt Instrument [Line Items]
Credit facility current credit amount			800,000,000	600,000,000
Line Of Credit Facility Commitment Amount [Member]
Debt Instrument [Line Items]
Credit facility current credit amount			$ 500,000,000	$ 250,000,000