Loans and Allowance for Loan Losses - Schedule of Average Balance of Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 103,551	$ 114,532	$ 102,507	$ 113,408
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	24,234	35,513	27,197	37,581
Average Recorded Investment with an allowance recorded	7,792	17,334	8,086	16,072
Commercial Real Estate - Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	33,268	40,971	31,258	37,937
Average Recorded Investment with an allowance recorded	30,846	15,119	28,580	15,977
Residential [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	2,482	1,233	2,405	1,270
Average Recorded Investment with an allowance recorded	1,011	1,099	1,059	1,072
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	1,755	878	1,786	865
Average Recorded Investment with an allowance recorded	$ 2,163	$ 2,385	$ 2,136	2,515
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with an allowance recorded				$ 119