Borrowing Arrangements (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified					12 Months Ended								3 Months Ended	12 Months Ended							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Credit Facility	Dec. 31, 2011 Senior Credit Facility	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent Maximum	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent Minimum	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent Federal funds rate	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent Bank of America prime rate	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent LIBOR	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent Base Rate	Dec. 31, 2012 Senior Credit Facility Bank of America as Administrative Agent LIBOR for base rate	Dec. 31, 2012 Senior Credit Facility Former Credit Agreement	Dec. 31, 2012 Senior Credit Facility Former Credit Agreement	Dec. 31, 2012 Revolving credit facility Bank of America as Administrative Agent	Dec. 31, 2012 Term loan facility Bank of America as Administrative Agent	Dec. 31, 2012 Other obligations	Dec. 31, 2011 Other obligations	Dec. 31, 2012 Obligations on seller notes and other	Dec. 31, 2011 Obligations on seller notes and other	Dec. 31, 2012 Convertible Debentures
Borrowing arrangements
Total debt	$ 310,559	$ 82,013	$ 307,939	$ 80,000													$ 1,725	$ 972	$ 895	$ 1,041
Less current portion	21,837	754
Long-term borrowings, excluding current portion	288,722	81,259
Total debt	310,474																				1,254
Senior Credit Facility
Maximum borrowing capacity					450,000										200,000	250,000
Amortization of principal in the first year																22,500
Amortization of principal in the second year																22,500
Amortization of principal in the third year																30,000
Amortization of principal in the fourth year																30,000
Amortization of principal in the fifth year																37,500
Amount borrowed															72,800
Period of total debt to EBITDA ratio					12 months
Variable rate basis								federal funds rate	Bank of America prime rate	LIBOR	base rate	LIBOR
Interest rate margin on variable rate basis (as a percent)								0.50%				1.00%
Total debt to EBITDA ratio that is required to be maintained						4.5
Fixed charge coverage ratio that is required to be maintained							1.25
Losses on the extinguishment of debt related to unamortized other comprehensive income on the interest rate cap														693
Losses on the extinguishment of debt related to debt issuance costs													51
Termination penalties														0
Weighted average interest rate on senior credit facility (as a percent)			3.70%	2.50%
Weighted average interest rate on outstanding borrowings, not including letters of credit (as a percent)	3.90%	3.90%
Letters of credit outstanding					56,006
Available borrowing capacity					$ 52,231
Redemption price (in dollars per share)																					$ 19.18