Reserves for unpaid losses and loss adjustment expenses Reconciliation of Claims Development to Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	$ 356,108
Reinsurance recoverable for unpaid losses	69,792	$ 55,389	$ 48,224
Unallocated claim adjustment expenses	34,158
Reserves for unpaid losses and loss adjustment expenses	460,058	$ 369,152	$ 315,717
Property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	5,507
Reinsurance recoverable for unpaid losses	3,119
Casualty - claims made [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	64,929
Reinsurance recoverable for unpaid losses	9,852
Casualty - occurrence [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for claims and claim adjustment expense, net	285,672
Reinsurance recoverable for unpaid losses	$ 56,821