Derivative Financial Instruments - Summary of Derivatives Designated as Hedges (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Notional amounts	$ 1,106,000,000	$ 665,500,000
Fixed Interest Swap | Derivatives designated as hedging instruments | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional amounts	$ 380,500,000	$ 130,500,000
Weighted average pay rates	0.20%	1.82%
Weighted average receive rates	1.33%	2.20%
Weighted average maturity (in years)	2 years 4 months 24 days	2 years 9 months 18 days
Fair value of swaps	$ 10,233,000	$ 1,555,000
Variable Interest Rate Swap | Derivatives designated as hedging instruments | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional amounts	$ 325,000,000	$ 25,000,000
Weighted average maturity (in years)	3 years 9 months 18 days	2 years 1 month 6 days
Weighted average pay rates	0.74%	3.52%
Weighted average receive rates	0.34%	1.93%
Unrealized gains (losses)	$ (2,222,000)	$ (954,000)
Variable Interest Rate Collar | Derivatives designated as hedging instruments | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional amounts	$ 300,000,000	$ 300,000,000
Weighted average cap rates	3.21%	3.21%
Weighted average floor rates	2.21%	2.21%
Weighted average rates	0.16%	1.70%
Weighted average maturity (in years)	1 year 1 month 6 days	1 year 10 months 24 days
Unrealized gains (losses)	$ 6,790,000	$ 3,691,000
Interest Rate Floor | Derivatives designated as hedging instruments | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional amounts	$ 100,000,000	$ 210,000,000
Weighted average floor rates	0.75%	2.00%
Weighted average sold floor rate		1.00%
Weighted average rates	0.16%	1.70%
Weighted average maturity (in years)	2 years 6 months	2 years 1 month 6 days
Unrealized gains (losses)	$ 1,590,000	$ 1,820,000