Other Income and Other Expense - Other Income and Other Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other income:
Credit-related fee income	$ 82,614	$ 77,580	$ 70,424
Other expense:
Professional services	312,998	$ 289,862	$ 268,060
Wilmington Trust Corporation [Member]
Other expense:
Accrual for Wilmington Trust Corporation legal-related matters	$ 135,000