Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Insurance	Jun. 30, 2018 Company
Organization And Summary Of Significant Accounting Policies [Line Items]
Number of insurance companies | Insurance	2
Number of companies acquired | Company		3
Corporate income tax rate	21.00%
Right-of-Use Asset	$ 44,615
Lease Liability Obligation	$ 53,616
Bracht, Deckers & Mackelbert NV and Assurances Continentales - Continentale Verzekeringen NV
Organization And Summary Of Significant Accounting Policies [Line Items]
Ownership interest in consolidated subsidiary	100.00%
Syndicate 1221
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage control of stamp capacity	100.00%
Navigators Holdings NV
Organization And Summary Of Significant Accounting Policies [Line Items]
Ownership interest in consolidated subsidiary	100.00%