Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	May 04, 2016 USD ($) Land	Dec. 31, 2016 USD ($) State	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Indefinite-lived Intangible Assets [Line Items]
Number of states in which company writes non-standard personal automobile insurance | State		17
Number of state in which company conducts servicing and underwriting operations | State		14
Maximum maturity period of cash equivalents included in investments		3 months
Restricted cash equivalents		$ 18,600,000	$ 9,400,000
Additional liability or reduction in deferred tax assets for unrecognized tax benefits		0	0
Foreclosed real estate held for sale assets		200,000	800,000
Tract of land sold | Land	1
Gain on sale of land	$ 1,200,000	1,237,000
Amortization expenses		18,900,000	16,300,000	$ 11,400,000
Identifiable intangible asset		7,600,000	8,500,000
Accumulated amortization expense		1,500,000	500,000
Estimated amortization expense, Year 1		800,000
Estimated amortization expense, Year 2		600,000
Estimated amortization expense, Year 3		500,000
Estimated amortization expense, Year 4		400,000
Estimated amortization expense, Year 5		300,000
Amount included in identifiable intangibles assets		7,626,000	8,491,000
Income taxes		200,000	700,000	700,000
Interest expense		4,200,000	$ 1,700,000	$ 1,700,000
Accounting Standards Update, 2015-05 | Software Licenses
Indefinite-lived Intangible Assets [Line Items]
Amount included in identifiable intangibles assets		$ 5,000
Minimum
Indefinite-lived Intangible Assets [Line Items]
Estimated useful lives of the assets		3 years
Maximum
Indefinite-lived Intangible Assets [Line Items]
Estimated useful lives of the assets		5 years