Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Business Acquisition [Line Items]
Cash paid for acquisition of businesses	$ 130.5	$ 0.0
Universal Weather And Aviation, Inc.
Business Acquisition [Line Items]
Cash paid for acquisition of businesses	131.0
Amounts due to sellers	30.0
Estimated purchase price	161.0
Assets acquired:
Accounts receivable	40.1
Goodwill and identifiable intangible assets	127.1
Other current and long-term assets	4.5
Liabilities assumed:
Accounts payable	(9.9)
Other current and long-term liabilities	(0.9)
Estimated purchase price	$ 161.0