Stockholders' Equity - Additional Information (Detail) - USD ($)	Jan. 01, 2020	Sep. 30, 2020	Dec. 31, 2019
Stockholders Equity [Line Items]
Increase to retained earnings for cumulative effect of adopting ASU		$ 846,934,000	$ 815,488,000
Small Business Administration (SBA), CARES Act, Paycheck Protection Program Lending Facility [Member]
Stockholders Equity [Line Items]
Percentage of risk weight under risk based capital rules		0.00%
Cumulative Effect, Period of Adoption, Adjustment [Member]
Stockholders Equity [Line Items]
Increase to retained earnings for cumulative effect of adopting ASU	$ 2,300,000
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Maximum [Member]
Stockholders Equity [Line Items]
Quantitative limit for trust preferred securities to be included in tier 1 capital		$ 15,000,000,000