Intangible Assets and Goodwill - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Weighted-average life	5 years 10 months 24 days
Customer Related Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average life	6 years
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average life	6 years
Mortgage Servicing Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average life	2 years