Other Income and Other Expense - Other Income and Other Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other income:
Credit-related fee income	$ 70,387	$ 86,792	$ 82,614
Other expense:
Professional services	240,047	330,900	312,998
Amortization of capitalized mortgage servicing rights	$ 84,821	$ 71,888	49,619
Wilmington Trust Corporation [Member]
Other expense:
Accrual for Wilmington Trust Corporation legal-related matters			$ 135,000