Borrowing Arrangements (Details) (USD $) In Thousands, unless otherwise specified					6 Months Ended					6 Months Ended			6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Revolving senior credit facility	Dec. 31, 2011 Revolving senior credit facility	Jun. 30, 2012 Revolving senior credit facility Existing and future domestic guarantor subsidiaries	Jun. 30, 2012 Revolving senior credit facility Existing and future foreign subsidiaries	Jun. 30, 2012 Revolving senior credit facility LIBOR	Jun. 30, 2012 Revolving senior credit facility LIBOR Low end of the range	Jun. 30, 2012 Revolving senior credit facility LIBOR High end of the range	Jun. 30, 2012 Revolving senior credit facility Base Rate	Jun. 30, 2012 Revolving senior credit facility Base Rate Low end of the range	Jun. 30, 2012 Revolving senior credit facility Base Rate High end of the range	Jun. 30, 2012 Revolving senior credit facility Overnight federal funds rate	Jun. 30, 2012 Revolving senior credit facility Bank of America, N.A. prime rate	Jun. 30, 2012 Letter of credit sub-facility	Jun. 30, 2012 Swing line sub-facility	Jun. 30, 2012 Capital lease obligations	Dec. 31, 2011 Capital lease obligations	Jun. 30, 2012 Obligations on seller notes and other	Dec. 31, 2011 Obligations on seller notes and other
Borrowing arrangements
Long-term borrowings	$ 71,668	$ 82,013	$ 70,000	$ 80,000													$ 699	$ 972	$ 969	$ 1,041
Less current portion	723	754
Long-term borrowings excluding current portion	70,945	81,259
Maximum borrowing capacity			210,000												50,000	10,000
Variable interest rate basis							One or two or three or six months LIBOR			Base Rate			federal funds	Prime rate
Variable interest rate margin (as a percent)								2.00%	3.50%		0.50%	2.00%	0.50%
Percentage of stock of subsidiaries pledged to secure debt					100.00%	65.00%
Weighted average interest rate on senior credit facility (as a percent)			2.60%	2.50%
Weighted average interest rate on outstanding borrowings, not including letters of credit (as a percent)			2.60%	2.60%
Letters of credit outstanding															17,823
Available borrowing capacity			$ 58,057