New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Jan. 01, 2018	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2020		Dec. 31, 2019		Jan. 01, 2019	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				$ 1,891,246		$ 1,672,438
Right-of-use asset				63,400		66,800
Lease liability				71,680		73,000
Cumulative effect adjustment			$ 2,228,470	3,016,948		2,606,440			$ 2,181,531
Reclassified stranded tax effects from AOCI to retained earnings			(4,974)
Allowance for credit losses			$ 103,635	215,973	[1]	101,788	[1]		100,604
Cumulative Effect Adjustments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment	$ 13					$ (7,039)	[2]		$ 145	[3]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201712Member
Accounting Standards Update 2016-01 [Member] | Cumulative Effect Adjustments [Member] | Revision of Prior Period, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment	$ 132
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset								$ 58,200
Lease liability								$ 63,000
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified stranded tax effects from AOCI to retained earnings		$ 12,900
ASU Nos. 2016-13 [Member] | Cumulative Effect Adjustments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				7,000
Allowance for credit losses				$ 9,000

[1] As of December 31, 2019, this line represents the Allowance for loan losses. See further discussion of this change in Note 2, “New Accounting Pronouncements”

[2] Related to the adoption of ASU No. 2016-13.  See Note 2, “New Accounting Pronouncements,” for further detail.

[3] Related to the adoption of ASU Nos. 2016-01 and 2017-12.  See Note 2, “New Accounting Pronouncements,” for further detail.