Acquisitions (First Quarter 2019) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration, current	$ 21,737	$ 22,538
Contingent consideration, non-current	$ 15,811	$ 17,170
Wenner Group, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jan. 01, 2019
Acquired entity, name	Wenner Group, LLC
Consideration paid in cash	$ 1,300
Contingent consideration	1,800
Contingent arrangements arising from acquisitions	1,800
Contingent consideration, current	600
Contingent consideration, non-current	1,200
Annual revenue	$ 2,400