Loans - Schedule of Purchased Credit Impaired Loans for which Payments Would Not be Collected (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable Impaired [Line Items]
Total loans	$ 1,850,364	$ 1,519,477
Purchased credit impairment loans, Net carrying amount	1,835,000	1,503,577
Commercial Loans [Member]
Financing Receivable Impaired [Line Items]
Total loans	708,364	504,258
Residential Mortgage Loans [Member]
Financing Receivable Impaired [Line Items]
Total loans	890,785	798,621
Consumer Loans [Member]
Financing Receivable Impaired [Line Items]
Total loans	251,215	$ 216,598
Purchased Credit Impaired Loans [Member]
Financing Receivable Impaired [Line Items]
Total loans	1,438
Purchased credit impairment loans, Net carrying amount	1,438
Purchased Credit Impaired Loans [Member] | Commercial Loans [Member]
Financing Receivable Impaired [Line Items]
Total loans	$ 1,438