Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended
	Jan. 01, 2020	Aug. 31, 2017	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Held-to-maturity securities, transferred security, at carrying value			$ 0	$ 11,544
Retained earnings			$ 1,100,097		$ 1,132,579
Cumulative Effect, Period of Adoption, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ (44,331)
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	57,442
Accounting Standards Update 2017-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Held-to-maturity securities, transferred security, at carrying value		$ 11,544
Decrease in AOCI due to transfer of held to maturity securities		$ 1,098
Accounting Standards Update 2018-10 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net lease assets	67,040
Net lease liabilities	70,692
Effect on retained earnings	$ 1,049