Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	May 04, 2016 USD ($) Land	Dec. 31, 2017 USD ($) State	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Indefinite-lived Intangible Assets [Line Items]
Number of states in which company writes non-standard personal automobile insurance | State		16
Number of state in which company conducts servicing and underwriting operations | State		13
Maximum maturity period of cash equivalents included in investments		3 months
Restricted cash equivalents		$ 18,500,000	$ 18,600,000
Additional liability or reduction in deferred tax assets for unrecognized tax benefits		0	0
Foreclosed real estate held for sale assets		200,000	200,000
Tract of land sold | Land	1
Gain on sale of land	$ 1,200,000		1,237,000
Amortization expenses		16,900,000	18,900,000	$ 16,300,000
Identifiable intangible asset		6,900,000	7,600,000
Accumulated amortization expense		2,300,000	1,500,000
Estimated amortization expense, Year 1		600,000
Estimated amortization expense, Year 2		500,000
Estimated amortization expense, Year 3		400,000
Estimated amortization expense, Year 4		300,000
Estimated amortization expense, Year 5		200,000
Undiscounted contractual cash payments remaining on leased properties		17,165,000
Income taxes		400,000	300,000	700,000
Interest expense		$ 4,400,000	$ 4,200,000	$ 1,700,000
ASU No. 2014-09
Indefinite-lived Intangible Assets [Line Items]
Percentage of total revenue subject to guidance		18.00%
Percentage of revenue related to commissions paid by third party insurance carriers		40.00%
Percentage of revenue related to commissions paid by third party ancillary insurance products		30.00%
Percentage of revenue from billing fees related to insurance contracts		30.00%
ASU No. 2016-02
Indefinite-lived Intangible Assets [Line Items]
Undiscounted contractual cash payments remaining on leased properties		$ 17,200,000
ASU No. 2018-02
Indefinite-lived Intangible Assets [Line Items]
Reclassification of deferred tax liability from accumulated other comprehensive income to accumulated deficit		$ 86,000
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