Acquisitions - Schedule of Estimated Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 489,039	$ 487,484
Pacific Coastal Pension and Insurance Services, Inc. (Pacific Coastal) [Member]
Business Acquisition [Line Items]
Accounts receivable, net	161
Identifiable intangible assets	897
Current liabilities	(309)
Total identifiable net assets	749
Goodwill	1,515
Aggregate purchase price	$ 2,264
Millimaki Eggert L L P [Member]
Business Acquisition [Line Items]
Accounts receivable, net			$ 325
Other assets			38
Identifiable intangible assets			1,005
Current liabilities			(49)
Total identifiable net assets			1,319
Goodwill			988
Aggregate purchase price			$ 2,307