Supplemental balance sheet and cash flow information (intangibles) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Intangibles [Line Items]
Gross carrying amount	$ 693,058	$ 595,488
Accumulated amortization	(407,747)	(388,308)
Net carrying amount	285,311	207,180
Amortization of intangibles	60,700	49,075	$ 46,651
Intangibles acquired	$ 139,212	$ 110,286	$ 54,575
Weighted-average amortization period (in years)	7 years	7 years	5 years
Estimated amortization expense
2016	$ 63,610
2017	49,487
2018	35,610
2019	27,698
2020	23,046
Internal-use software [Member]
Intangibles [Line Items]
Intangibles acquired	$ 35,945	$ 33,867	$ 34,455
Weighted-average amortization period (in years)	4 years	4 years	3 years
Customer lists/relationships [Member]
Intangibles [Line Items]
Intangibles acquired	$ 101,867	$ 45,869	$ 16,610
Weighted-average amortization period (in years)	8 years	9 years	8 years
Trade names [Member]
Intangibles [Line Items]
Intangibles acquired	$ 1,400	$ 2,000	$ 200
Weighted-average amortization period (in years)	2 years	3 years	2 years
Software to be sold [Member]
Intangibles [Line Items]
Intangibles acquired	$ 0	$ 28,500	$ 0
Weighted-average amortization period (in years)		9 years
Other [Member]
Intangibles [Line Items]
Intangibles acquired	0	$ 50	$ 3,310
Weighted-average amortization period (in years)		2 years	4 years
Indefinite-lived intangibles [Member] | Trade names [Member]
Intangibles [Line Items]
Gross carrying amount	19,100	$ 19,100
Net carrying amount	19,100	19,100
Amortizable intangibles [Member]
Intangibles [Line Items]
Gross carrying amount	673,958	576,388
Accumulated amortization	(407,747)	(388,308)
Net carrying amount	266,211	188,080
Amortizable intangibles [Member] | Internal-use software [Member]
Intangibles [Line Items]
Gross carrying amount	375,037	364,229
Accumulated amortization	(310,665)	(303,340)
Net carrying amount	64,372	60,889
Amortization of intangibles	31,752	34,282	$ 32,555
Amortizable intangibles [Member] | Customer lists/relationships [Member]
Intangibles [Line Items]
Gross carrying amount	202,682	106,218
Accumulated amortization	(54,990)	(40,097)
Net carrying amount	147,692	66,121
Amortizable intangibles [Member] | Trade names [Member]
Intangibles [Line Items]
Gross carrying amount	64,881	69,281
Accumulated amortization	(36,325)	(37,623)
Net carrying amount	28,556	31,658
Amortizable intangibles [Member] | Software to be sold [Member]
Intangibles [Line Items]
Gross carrying amount	28,500	28,500
Accumulated amortization	(3,765)	(601)
Net carrying amount	24,735	27,899
Amortization of intangibles	3,164	601	0
Amortizable intangibles [Member] | Other [Member]
Intangibles [Line Items]
Gross carrying amount	2,858	8,160
Accumulated amortization	(2,002)	(6,647)
Net carrying amount	856	1,513
Amortizable intangibles [Member] | Other amortizable intangibles [Member]
Intangibles [Line Items]
Amortization of intangibles	$ 25,784	$ 14,192	$ 14,096