Reinsurance - Schedule of Catastrophe Losses by Event Magnitude (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) catastrophic_event	Mar. 31, 2016 USD ($) catastrophic_event
Catastrophe
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	5	10
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 10,612	$ 15,056
Catastrophic Events, Impact on Combined Ratio	9.90%	14.90%
Catastrophe | Catastrophe Loss Size, Range 2 [Member]
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	4	4
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 9,873	$ 11,341
Catastrophic Events, Impact on Combined Ratio	9.20%	11.20%
Catastrophe | Catastrophe Loss Size, Range 1 [Member]
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	1	6
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 739	$ 3,715
Catastrophic Events, Impact on Combined Ratio	0.70%	3.70%
Minimum | Catastrophe Loss Size, Range 3 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 5,000	$ 5,000
Minimum | Catastrophe Loss Size, Range 2 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	1,000	1,000
Minimum | Catastrophe Loss Size, Range 1 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	0	0
Maximum | Catastrophe Loss Size, Range 3 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	10,000	10,000
Maximum | Catastrophe Loss Size, Range 2 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	5,000	5,000
Maximum | Catastrophe Loss Size, Range 1 [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 1,000	$ 1,000