Acquisitions (First Quarter 2017) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration, current		$ 16,293	$ 15,151
Contingent consideration, non-current		28,331	22,423
Goodwill		551,367	$ 528,424
Pacific Coastal Pension and Insurance Services, Inc. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Feb. 01, 2017
Acquired entity, name	Pacific Coastal Pension and Insurance Services, Inc.
Consideration paid in cash	$ 600
Contingent consideration	1,700
Contingent consideration, current	500
Contingent consideration, non-current	1,200
Annual revenue	1,400
Goodwill	$ 1,515	$ 22,943