Goodwill and Other Amortizing Intangible Assets - Additional Information (Detail) - USD ($)		12 Months Ended
	Sep. 06, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill And Other Intangibles [Line Items]
Goodwill		$ 303,328,000	$ 303,328,000
Impairment charges on goodwill		0	0	$ 0
Servicing Asset		1,900,000	1,300,000
Total amortization		13,223,000	13,100,000
Intangible amortization		3,689,000	3,344,000	3,217,000
Servicing Asset at Amortized Cost, Amortization		$ 300,000	200,000
Customer deposit intangibles
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period		8 years 8 months 12 days
Core deposits weighted average amortization period		7 years 1 month 6 days
Total amortization		$ 11,653,000	11,760,000
Customer list intangible
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period		8 years 8 months 12 days
Core deposits weighted average amortization period		6 years 9 months 18 days
Total amortization		$ 1,570,000	1,340,000
Customer-Related Intangible Assets [Member]
Goodwill And Other Intangibles [Line Items]
Intangible amortization		$ 3,400,000	$ 3,200,000	$ 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