Long-Term Debt And Notes Payable (Narrative) (Details) (USD $)	1 Months Ended			3 Months Ended	12 Months Ended				1 Months Ended									1 Months Ended
	Dec. 31, 2012	May 31, 2012	Nov. 30, 2006	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 4.45% Notes Due 2023 [Member]	Dec. 31, 2013 2.75% Notes Due 2018 [Member]	Dec. 31, 2013 Bank Loan Commitments [Member]	Dec. 31, 2013 Amended and Restated Credit Agreement Due to Expire in May 2017 [Member]	Dec. 31, 2013 5.50% Notes Due 2013 [Member]		Dec. 31, 2012 5.50% Notes Due 2013 [Member]		Sep. 30, 2003 5.50% Notes Due 2013 [Member]	Nov. 30, 2006 6.55% Notes Due 2036 [Member]	Dec. 31, 2013 6.55% Notes Due 2036 [Member]	Dec. 31, 2012 6.55% Notes Due 2036 [Member]	May 31, 2012 London Interbank Offered Rate (LIBOR) [Member] Minimum [Member]	May 31, 2012 London Interbank Offered Rate (LIBOR) [Member] Maximum [Member]	May 31, 2012 Federal Funds Rate [Member]	May 31, 2012 Adjusted London Interbank Offered Rate [Member]	May 31, 2012 Adjusted London Interbank Offered Rate [Member] Minimum [Member]	May 31, 2012 Adjusted London Interbank Offered Rate [Member] Maximum [Member]
Debt Instrument [Line Items]
Notes issued, term									10 years	5 years								30 years
Notes issued									$ 300,000,000	$ 250,000,000								$ 200,000,000
Notes maturity date			Nov. 15, 2036
Debt instrument interest rate									4.45%	2.75%							5.50%	6.55%
Amended and restated credit agreement duration, years		5 years
Line of credit facility, maximum borrowing capacity	400,000,000	300,000,000				400,000,000					600,000,000
Line of credit facility, amended maximum borrowing capacity	500,000,000					500,000,000
Long-term debt	399,092,000				749,170,000	399,092,000			299,976,000	249,965,000		125,000,000	0	[1]	199,898,000	[1]			199,229,000	199,194,000
Line of Credit Facility, Term	364 days
Line of credit facility, borrowing capacity expansion	200,000,000					200,000,000
Basis spread on variable rate																					1.05%	1.475%	0.50%	1.00%	0.05%	0.475%
Total debt to capitalization ratio					0.42			0.65
Percentage of principal amount Company may be required to buy back at									101.00%	101.00%								101.00%
Annualized interest rate including debt issuance cost amortization									4.56%	2.92%									6.67%
Senior Notes				200,000,000
Repayments of Long-term Debt				90,000,000	200,000,000	0	0
Repayment of Long-term Debt Using Multi-year Credit Facility Borrowings				110,000,000
Date of unsecured notes issued					Apr. 01, 1991
Standby letters of credit					28,000,000
Uncommitted letter of credit reimbursement agreement					$ 60,000,000

[1] As of December 31, 2012, the Company classified the notes which mature in 2013 as long-term debt due to the Company's intent to refinance on a long-term basis and the ability to utilize the existing five-year $300 million Amended and Restated Credit Agreement.