Long-Term Debt and Credit Agreements (Details) (USD $)	12 Months Ended				1 Months Ended					1 Months Ended			0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 22, 2013	Jan. 31, 2014 Senior Notes [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2011 Revolving Credit Facility [Member]	Dec. 31, 2003 Unsecured Senior Notes [Member]	Dec. 31, 2013 6.81% Senior Unsecured Notes [Member] Unsecured Senior Notes [Member]	Dec. 31, 2003 6.81% Senior Unsecured Notes [Member] Unsecured Senior Notes [Member]	Oct. 22, 2013 Senior Unsecured Note [Member]	Oct. 22, 2013 5.25 Senior Unsecured Note [Member] Senior Notes [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Oct. 22, 2013 Minimum [Member]	Oct. 22, 2013 Minimum [Member] Senior Unsecured Note [Member]	Oct. 22, 2013 Maximum [Member]	Oct. 22, 2013 Maximum [Member] Senior Unsecured Note [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit								$ 180,000,000						$ 200,000,000.0
Remaining borrowing capacity under line of credit						161,200,000
Average interest rate on debt instruments						3.71%	3.81%
Unamortized debt issuance expense	853,000	0
Face amount of debt instruments									100,000,000			100,000,000			11,000,000		40,000,000
Stated interest rate of debt instruments (as a percentage)				5.25%							6.81%					4.67%		5.45%
Amounts repaid on long-term debt	35,000,000	27,258,000	305,000							35,000,000
Amount outstanding on letters of credit	4,600,000
Proceeds from issuance of long-term debt					89,000,000								11,000,000
Long-term debt, excluding unamortized deferred financing costs	$ 44,347,000	$ 92,814,000