Principles of Consolidation and Basis of Presentation - Additional Information (Detail) $ in Thousands		9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Segment Product
Organization And Basis Of Presentation [Line Items]
Date of incorporation			Feb. 09, 2016
State of incorporation			Cayman Islands
Kind of listing			A ordinary shares
Date of liquidation			Nov. 07, 2016
Number of business segments | Segment			3
Proceeds from sale of capital stock	$ 18,700	$ 18,700
Pretax gain on sale of capital stock	$ 6,900	$ 6,900	$ 6,857
Commercial Lines Segment
Organization And Basis Of Presentation [Line Items]
Number of product classifications | Product			3