Goodwill and Other Intangible Assets - Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, beginning balance	$ 172,559	$ 172,559
Goodwill, acquired during period	0	0
Goodwill, ending balance	172,559	172,559
Banking [Member]
Goodwill [Line Items]
Goodwill, beginning balance	138,476	138,476
Goodwill, acquired during period	0	0
Goodwill, ending balance	138,476	138,476
Wealth Management [Member]
Goodwill [Line Items]
Goodwill, beginning balance	15,434	15,434
Goodwill, acquired during period	0	0
Goodwill, ending balance	15,434	15,434
Insurance [Member]
Goodwill [Line Items]
Goodwill, beginning balance	18,649	18,649
Goodwill, acquired during period	0	0
Goodwill, ending balance	$ 18,649	$ 18,649