Reinsurance - Schedule of Unsecured Reinsurance Recoverables from Reinsurers (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	$ 83,666	$ 91,077
Funds withheld and letters of credit related to the above recoverables	(38,453)
Total unsecured amounts recoverable from reinsurers	45,213
Reinsurance Recoverable [Member] | Reinsurer Concentration Risk [Member]
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	83,666
Reinsurance Recoverable [Member] | Reinsurer Concentration Risk [Member] | Hannover Reinsurance Limited (Ireland) (A+) [Member]
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	29,670
Reinsurance Recoverable [Member] | Reinsurer Concentration Risk [Member] | Odyssey America Reinsurance Corporation (A) [Member]
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	12,600
Reinsurance Recoverable [Member] | Reinsurer Concentration Risk [Member] | Minnesota Workers' Compensation Reinsurance Association (NR) [Member]
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	9,623
Reinsurance Recoverable [Member] | Reinsurer Concentration Risk [Member] | Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Amounts recoverable from reinsurers	$ 31,773