Recent Accounting Pronouncements - Additional Information (Detail) $ in Thousands		6 Months Ended
	Jan. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)		Jun. 30, 2020 portfolio	Jun. 30, 2020 segment	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)		Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of distinct loan portfolios | portfolio				7
Current expected credit losses, initial loss forecast		1 year
Current expected credit losses, reversion period, term		2 years
Increase in allowance for loan loss	$ 54,619	$ 128,394	[1]			$ 106,380	$ 54,619	[1]	$ 56,292	$ 55,559	$ 55,461
Increase in allowance for credit losses on unfunded loan	2,656	11,026				8,950	2,656
Decrease in retained earnings	(682,185)	$ (678,378)					(682,185)
Noncredit discount amount accreted into interest income	11,800
Number of loan portfolios | portfolio				4
Number of loan segments				7	7
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in allowance for loan loss	41,347					$ 0
Increase in allowance for credit losses on unfunded loan	4,549						$ 4,549
Decrease in retained earnings	31,150
Impact of ASC 326 Adoption | Acquired Loan Portoflio
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in allowance for loan loss	$ 27,100

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.