Long-Term Debt and Short-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of long-term debt and short-term debt
Total debt	$ 75,041	$ 78,132
Less current maturities of long-term debt	6,326	6,503
Long-term debt, excluding current maturities of long-term debt	68,715	71,629
December 21, 2014 [Member]
Summary of long-term debt and short-term debt
Borrowings under our $100,000 revolving credit facility bearing interest at a floating rate equal to LIBOR (0.25% at September 30, 2012) plus an applicable margin of 2.75% at September 30, 2012, expiring December 21, 2014.	43,612	40,989
April 26, 2014 [Member]
Summary of long-term debt and short-term debt
Borrowings under our $40,000 aggregate principal amount of fixed rate notes bearing interest at a fixed rate of 5.39% maturing on April 26, 2014. Annual principal payments of $5,714 began on April 26, 2008 and extend through the date of maturity.	11,429	17,143
December 20, 2018 [Member]
Summary of long-term debt and short-term debt
Borrowings under our $20,000 aggregate principal amount of fixed rate notes bearing interest at a fixed rate of 4.64% maturing on December 20, 2018. Annual principal payments of $4,000 will begin on December 22, 2014 and extend through the date of maturity.	$ 20,000	$ 20,000