Unpaid Loss and Loss Adjustment Expenses Incurred loss & allocated loss adjustment expenses, net of reinsurance (Details) - USD ($)

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Jun. 30, 2018

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

$ 2,500,000

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 139,316,000

Accident Year 2009 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

4,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

40,085,000

$ 40,091,000

$ 40,177,000

$ 40,211,000

$ 40,308,000

$ 40,436,000

$ 40,219,000

$ 38,486,000

$ 37,387,000

$ 35,209,000

Accident Year 2010 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

2,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

53,689,000

53,693,000

53,810,000

53,993,000

54,021,000

54,591,000

55,120,000

51,951,000

47,253,000

Accident Year 2011 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

15,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

27,851,000

27,597,000

27,613,000

27,865,000

28,094,000

28,744,000

29,458,000

29,034,000

Accident Year 2012 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

9,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

13,037,000

12,720,000

12,815,000

12,926,000

13,273,000

13,536,000

13,736,000

Accident Year 2013 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

228,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

4,654,000

4,617,000

4,488,000

5,474,000

6,434,000

6,456,000

Accident Year 2014 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

29,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Accident Year 2015 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Accident Year 2016 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Accident Year 2017 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Accident Year 2018 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Commercial auto liability [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

33,715,000

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

34,061,000

Commercial auto liability [Member] | Accident Year 2009 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

8,767,000

8,765,000

8,747,000

8,638,000

8,533,000

8,326,000

7,926,000

5,005,000

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

2,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

7,585,000

7,591,000

7,612,000

7,625,000

7,662,000

7,738,000

7,743,000

7,016,000

6,739,000

10,450,000

Commercial auto liability [Member] | Accident Year 2010 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

7,943,000

7,681,000

7,457,000

7,150,000

7,028,000

6,607,000

5,034,000

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

26,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

9,181,000

9,185,000

9,197,000

9,215,000

9,214,000

9,351,000

9,711,000

8,745,000

8,205,000

Commercial auto liability [Member] | Accident Year 2011 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

284,000

358,000

352,000

299,000

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

2,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

8,901,000

8,816,000

8,812,000

8,791,000

8,752,000

8,990,000

9,784,000

8,521,000

Commercial auto liability [Member] | Accident Year 2012 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

163,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

8,078,000

7,766,000

7,562,000

7,349,000

7,548,000

7,759,000

9,503,000

Commercial auto liability [Member] | Accident Year 2013 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

58,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

316,000

364,000

350,000

489,000

477,000

597,000

Commercial auto liability [Member] | Accident Year 2014 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

26,000

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Commercial auto liability [Member] | Accident Year 2015 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Commercial auto liability [Member] | Accident Year 2016 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Commercial auto liability [Member] | Accident Year 2017 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Commercial auto liability [Member] | Accident Year 2018 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

Auto physical damage [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

18,177

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

18,177

Auto physical damage [Member] | Accident Year 2009 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

3,261

3,269

3,267

3,266

3,270

3,268

2,971

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

6,482

6,480

6,482

6,476

6,458

6,451

6,857

7,343

$ 9,829

Auto physical damage [Member] | Accident Year 2010 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

1,908

2,018

2,017

2,016

2,006

1,951

1,783

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

5,538

5,535

5,532

5,518

5,487

5,499

6,192

$ 7,977

Auto physical damage [Member] | Accident Year 2011 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

988

1,002

1,001

1,015

1,050

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

3,261

3,269

3,260

3,262

3,263

3,241

3,247

$ 4,366

Auto physical damage [Member] | Accident Year 2012 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

1,908

2,018

2,007

2,015

1,990

1,920

$ 1,755

Auto physical damage [Member] | Accident Year 2013 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

988

1,003

999

1,001

996

$ 1,085

Auto physical damage [Member] | Accident Year 2014 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 0

Auto physical damage [Member] | Accident Year 2015 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 0

Auto physical damage [Member] | Accident Year 2016 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 0

Auto physical damage [Member] | Accident Year 2017 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 0

Auto physical damage [Member] | Accident Year 2018 [Member]

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount

Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount

SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses

$ 0