Goodwill and Other Amortizing Intangible Assets - Additional Information (Detail) - USD ($)		12 Months Ended
	Sep. 06, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Other Intangibles [Line Items]
Goodwill		$ 303,328,000	$ 274,202,000
Goodwill, Acquired During Period		29,100,000
Impairment charges on goodwill		0	0	$ 0
Servicing Asset		1,300,000	500,000
Total amortization		13,100,000	9,946,000
Intangible amortization		3,344,000	3,217,000	3,081,000
Servicing Asset at Amortized Cost, Amortization		$ 200,000	100,000
Customer deposit intangibles
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period		9 years 8 months 12 days
Core deposits weighted average amortization period		8 years 1 month 6 days
Total amortization		$ 11,760,000	8,877,000
Customer list intangible
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period		9 years 8 months 12 days
Core deposits weighted average amortization period		7 years 10 months 24 days
Total amortization		$ 1,340,000	1,069,000
Customer-Related Intangible Assets [Member]
Goodwill And Other Intangibles [Line Items]
Intangible amortization		$ 3,200,000	$ 3,100,000	$ 3,100,000
Santander Bank, N.A. [Member]
Goodwill And Other Intangibles [Line Items]
Goodwill, Acquired During Period	$ 29,126,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 5,615,000