Loans - Carrying Amount of Purchased Credit Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable Impaired [Line Items]
Beginning Balance	$ 1,503,577
Loans purchased during the year	15,189	$ 8,681
Ending Balance	1,835,000
Purchased Credit Impaired Loans [Member]
Financing Receivable Impaired [Line Items]
Loans purchased during the year	1,797
Ending Balance	$ 1,438