Reinsurance - Schedule of Catastrophe Losses by Event Magnitude (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2017 USD ($) catastrophic_event	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) catastrophic_event	Mar. 31, 2016 USD ($)	Jun. 30, 2017 USD ($) catastrophic_event	Jun. 30, 2016 USD ($) catastrophic_event
Catastrophe
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	15		16		15	16
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 21,798		$ 3,720		$ 32,410	$ 18,776
Catastrophic Events, Impact on Combined Ratio	13.70%		3.30%		12.10%	8.70%
Catastrophe | Catastrophe Loss Size, Range 3 [Member]
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event					1	0
Catastrophic Event, Incurred Losses and Loss Adjustment Expense					$ 6,963	$ 0
Catastrophic Events, Impact on Combined Ratio					2.60%	0.00%
Catastrophe | Catastrophe Loss Size, Range 2 [Member]
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	6		4		8	9
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 17,110		$ 5,688		$ 21,056	$ 14,789
Catastrophic Events, Impact on Combined Ratio	10.80%		5.00%		7.90%	6.90%
Catastrophe | Catastrophe Loss Size, Range 1 [Member]
Liability for Catastrophe Claims [Line Items]
Number of Catastrophic Events | catastrophic_event	9		12		6	7
Catastrophic Event, Incurred Losses and Loss Adjustment Expense	$ 4,688		$ (1,968)		$ 4,391	$ 3,987
Catastrophic Events, Impact on Combined Ratio	2.90%		(1.70%)		1.60%	1.80%
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