Fair Value Disclosures - Contingent Consideration Liability Change in Amount (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in Contingent Consideration Liability [Roll Forward]
Beginning Balance	$ 5,999	$ 5,577
Contingent Consideration from New Acquisition	0	0	$ 1,525
Payment of Contingent Consideration	5,413	2,552
Adjustment of Contingent Consideration	(247)	2,974
Ending Balance	339	5,999	5,577
Sterner Insurance Associates Inc [Member]
Change in Contingent Consideration Liability [Roll Forward]
Beginning Balance	331	1,144
Contingent Consideration from New Acquisition	0	0
Payment of Contingent Consideration	30	1,325
Adjustment of Contingent Consideration	(301)	512
Ending Balance	0	331	1,144
Girard Partners [Member]
Change in Contingent Consideration Liability [Roll Forward]
Beginning Balance	5,668	4,241
Contingent Consideration from New Acquisition	0	0
Payment of Contingent Consideration	5,383	967
Adjustment of Contingent Consideration	54	2,394
Ending Balance	339	5,668	4,241
John T Fretz Insurance Agency [Member]
Change in Contingent Consideration Liability [Roll Forward]
Beginning Balance	$ 0	192
Contingent Consideration from New Acquisition		0
Payment of Contingent Consideration		260
Adjustment of Contingent Consideration		68
Ending Balance		$ 0	$ 192