Business Combinations - Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 82.4	$ 7.8	$ 34.2
Business Combination Pro Forma Information Income Loss Before Income Taxes Of Acquiree Since Acquisition Date Actual	$ 6.3	$ 2.4	$ 4.3
Two Thousand Seventeen Acquisition [Member] [Domain]
Net income per share:
Basic (in dollars per share)		$ 1.44	$ 0.93
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax, Per Share, Diluted		$ 1.41	$ 0.92
Weighted Average Basic Shares Outstanding, Pro Forma		272,580	272,278
Weighted average number of shares outstanding:
Pro Forma Weighted Average Shares Outstanding, Diluted		277,586	275,608