Fair value measurements (recurring and nonrecurring fair value measurements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair value disclosure, hedge ineffectiveness [Abstract]
(Loss) gain from derivatives		$ 2,220	$ 5,608	$ (152)
Loss from change in fair value of hedged debt		(2,395)	(5,133)	254
Net decrease (increase) in interest expense		(175)	475	102
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment charges	1,196	1,196	0	24,900
Long-term investment in mutual funds	2,165	2,165	2,283
Net unrealized gain on investment in mutual funds			196	420
Fair Value, Measurements, Nonrecurring [Member] | Impairment of Intangible Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill				20,000	[1]
Assets held for sale	1,196	1,196
Indefinite-lived trade name				4,900	[2]
Total impairment charges		1,196		24,900
Fair Value, Measurements, Nonrecurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill				20,245	[1]
Assets held for sale	2,741	2,741
Indefinite-lived trade name				19,100	[2]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill				0	[1]
Indefinite-lived trade name				0	[2]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill				0	[1]
Assets held for sale	2,741	2,741
Indefinite-lived trade name				0	[2]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill				20,245	[1]
Assets held for sale	0	0
Indefinite-lived trade name				19,100	[2]
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - funds held for customers	5,418	5,418	10,249
Marketable securities - corporate investments	2,001	2,001	2,029
Long-term investment in mutual funds	2,165	2,165	2,283
Derivative assets	4,539	4,539	5,456
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - funds held for customers	0	0	0
Marketable securities - corporate investments	0	0	0
Long-term investment in mutual funds	2,165	2,165	2,283
Derivative assets	0	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - funds held for customers	5,418	5,418	10,249
Marketable securities - corporate investments	2,001	2,001	2,029
Long-term investment in mutual funds	0	0	0
Derivative assets	4,539	4,539	5,456
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - funds held for customers	0	0	0
Marketable securities - corporate investments	0	0	0
Long-term investment in mutual funds	0	0	0
Derivative assets	$ 0	$ 0	$ 0

[1] Represents the implied fair value of the goodwill assigned to the reporting unit for which we were required to calculate this amount.

[2] Represents the fair value determined from the event-driven impairment analysis completed during the quarter ended March 31, 2009.