Fair value measurements (acquisitions) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($)
Acquisitions [Line Items]
Intangibles acquired	$ 48,898
2016 acquisitions [Member]
Acquisitions [Line Items]
Intangibles acquired	32,332
Customer lists/relationships [Member]
Acquisitions [Line Items]
Intangibles acquired	31,082
Customer lists/relationships [Member] | 2016 acquisitions [Member]
Acquisitions [Line Items]
Intangibles acquired	$ 31,082