Revolving Credit Facility (Details) (USD $)			9 Months Ended					9 Months Ended				9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Revolving Credit Facility multiplier	Sep. 30, 2013 Revolving Credit Facility Minimum	Sep. 30, 2013 Revolving Credit Facility Maximum	Sep. 30, 2013 Revolving Credit Facility Prime rate	Sep. 30, 2012 Revolving Credit Facility Prime rate	Sep. 30, 2013 Revolving Credit Facility Prime rate Minimum	Sep. 30, 2013 Revolving Credit Facility Prime rate Maximum	Sep. 30, 2013 Revolving Credit Facility LIBOR	Sep. 30, 2012 Revolving Credit Facility LIBOR	Sep. 30, 2013 Revolving Credit Facility LIBOR Minimum	Sep. 30, 2013 Revolving Credit Facility LIBOR Maximum
Revolving credit facility
Revolving credit limit			$ 125,000,000
Potential future expansion of the Facility under accordion feature			175,000,000
Variable rate basis						Bank's prime rate plus a margin				LIBOR
Interest rate margin per debt instrument (as a percent)								1.25%	2.25%			2.25%	3.25%
Actual interest rate margin (as a percent)						1.25%				2.25%
Weighted average interest rate (as a percent)						4.50%	4.50%			2.53%	2.72%
Quarterly commitment fee on the average daily unused facility balance (as a percent)				0.30%	0.50%
EBITDA multiplier			3.0
Percentage of acquired EBITDA which can be included in covenants calculation					50.00%
Borrowing capacity permitted to be used per formula			73,100,000
Amount outstanding			0
Irrevocable letters of credit outstanding			5,500,000
Remaining borrowing capacity available for use			66,700,000
Minimum net worth required to be maintained			160,500,000
Company's net worth	$ 213,695,000	$ 204,315,000