Reinsurance - Schedule of allowance for uncollectible reinsurance (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Allowance for uncollectible reinsurance [Abstract]
Allowance relating to unpaid loss and loss expense recoverables	$ 41,103	$ 42,119
Allowance relating to reinsurance balances receivable	22,733	20,710
Total allowance for uncollectible reinsurance	$ 63,836	$ 62,829

Amount of valuation allowance for reinsurance recoverables for losses reported to the ceding insurer but not yet paid, and for amounts expected based upon statistical projections and other measures of incurred losses and loss settlement expenses which have not yet been reported to the ceding insurer.

No definition available.

Name:	us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant