Loans - Carrying Amount of Purchased Credit Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable Impaired [Line Items]
Beginning Balance	$ 2,197,285
Loans purchased during the period	46,669	$ 26,489
Ending Balance	$ 2,268,494
Purchased Credit Impaired Loans [Member]
Financing Receivable Impaired [Line Items]
Beginning Balance		1,194
Ending Balance		$ 1,083