Acquisitions - Preliminary Allocation of Purchase Price (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets:
Goodwill	$ 715,359	$ 586,665	$ 519,203
Nubera and Capterra
Assets:
Cash	10,700
Receivables and other assets	12,800
Amortizable intangible assets	79,600
Goodwill	138,100
Total assets	241,200
Liabilities:
Payables and accrueds	34,300
Total liabilities	34,300
Net assets acquired	206,900
Capterra
Assets:
Amortizable intangible assets	68,500
Goodwill	121,100
Liabilities:
Payables and accrueds	25,600
Nubera
Assets:
Amortizable intangible assets	11,100
Goodwill	$ 17,000