Reinsurance - Gross Quota and Net Quota Share Reinsurance - Additional information - (Detail) - NBIC [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Gross Quota Share [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Percentage of gross quota share		8.00%
Reinsurance recoveries on paid losses		$ 1,000.0
2020-2021 Net Quota Share Reinsurance [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Net lines quota share occurrence limit	$ 20.0
Percentage of renewed ceded net premium and losses			56.00%	5.00%