Qualified Affordable Housing Projects and Other Tax Credit Investments - Schedule of Qualified Affordable Housing Projects and Other Tax Credit Investments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Investment Holdings [Line Items]
Total	$ 53,289		$ 54,404
Total	27,928		38,548
Amortization Expense	1,052	$ 1,355
Tax Expense (Benefit) Recognized	(1,286)	(6,194)
LIHTC [Member]
Investment Holdings [Line Items]
Proportional amortization method of investment	27,554		28,396
Unfunded commitment, Proportional amortization	1,365		2,238
Amortization Expense	792	639
Tax Expense (Benefit) Recognized	(1,042)	(831)
FHTC [Member]
Investment Holdings [Line Items]
Equity method investment	16,815		16,815
Unfunded commitment, Equity	17,027		17,945
Tax Expense (Benefit) Recognized		(1,948)
CReED [Member]
Investment Holdings [Line Items]
Equity method investment	13		17
Unfunded commitment, Equity			538
Renewable Energy [Member]
Investment Holdings [Line Items]
Equity method investment	8,907		9,176
Unfunded commitment, Equity	9,536		$ 17,827
Amortization Expense	260	716
Tax Expense (Benefit) Recognized	$ (244)	$ (3,415)