Supplemental balance sheet and cash flow information (other) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in contract acquisition costs
Balance, beginning of year		$ 65,792	$ 58,792	$ 74,101
Additions	[1]	18,224	27,506	6,999
Amortization		(19,969)	(20,185)	(18,741)
Other		(152)	(321)	(3,567)
Balance, end of year		63,895	65,792	58,792
Contract acquisition payments		27,079	23,068	12,806
Accrued liabilities
Funds held for customers		85,091	86,799
Deferred revenue		47,021	48,049
Employee profit sharing/cash bonus		31,312	27,760
Acquisition-related liabilities	[2]	23,878	12,763
Income tax		17,827	19,708
Contract acquisition costs due within one year		11,670	12,426
Customer rebates		11,508	16,281
Restructuring due within one year (Note 8)		4,380	4,181
Other		44,566	45,082
Accrued liabilities		277,253	273,049
Other non-current liabilities
Contract acquisition costs		21,658	29,855
Acquisition-related liabilities	[2]	2,042	19,390
Other		28,541	30,461
Other non-current liabilities		52,241	79,706
Supplemental cash flow information
Income taxes paid		124,878	97,309	110,999
Interest paid		19,465	20,975	24,286
Non-cash investing activities [Line Items]
Proceeds from sales of businesses - notes receivable		24,497	0	12,475
2017 acquisitions [Member]
Non-cash investing activities [Line Items]
Acquisition-related liabilities	[2]	$ 5,855
2016 acquisitions [Member]
Non-cash investing activities [Line Items]
Acquisition-related liabilities	[2]		$ 27,441
2015 acquisitions [Member]
Non-cash investing activities [Line Items]
Acquisition-related liabilities	[2]			$ 7,450

[1] Contract acquisition costs are accrued upon contract execution. Cash payments made for contract acquisition costs were $27,079 for 2017, $23,068 for 2016 and $12,806 for 2015.

[2] Consists of holdback payments due at future dates and liabilities for contingent consideration. Further information regarding liabilities for contingent consideration can be found in Note 7.