Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Days from origination after which mortgage loan are sold	30 days
Loan upon which a default of principal or interest has existed for a period	90 days
Intangible assets, Estimated useful lives	5 years 10 months 24 days
Excess tax benefit from share-based compensation	$ 2,601
Accounting Standards Update 2016-09 [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Excess tax benefit from share-based compensation	$ 2,600
Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	6 years
Minimum [Member] | Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	7 years
Minimum [Member] | Customer Relationship Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	3 years
Maximum [Member] | Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	10 years
Maximum [Member] | Customer Relationship Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	18 years
Home Equity Lines of Credit [Member] | Maximum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	8.00%
First Liens [Member] | Minimum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	82.00%
Junior Liens [Member] | Maximum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	10.00%