Reserves for unpaid losses and loss adjustment expenses Reconciliation of Claims Development to Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	$ 280,422
Reinsurance recoverable for unpaid losses	55,389	$ 48,224	$ 70,199
Unallocated claim adjustment expenses	33,341
Reserves for unpaid losses and loss adjustment expenses	369,152	$ 315,717	$ 264,801
Property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	2,942
Reinsurance recoverable for unpaid losses	1,133
Casualty - claims made [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	50,461
Reinsurance recoverable for unpaid losses	7,617
Casualty - occurrence [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	227,019
Reinsurance recoverable for unpaid losses	$ 46,639