Investments - Schedule of Available-for-sale Securities Reconciliation (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities
Gross unrealized gains	$ 260
Gross unrealized loss	0
Fair Value	836,390	$ 762,855
Equity securities fair value	93,092	63,295
U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	104,822	93,827
Gross unrealized gains	0	40
Gross unrealized loss	2,093	1,241
Fair Value	102,729	92,626
Foreign Government
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	2,998	2,022
Gross unrealized gains	0	14
Gross unrealized loss	32	0
Fair Value	2,966	2,036
States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	154,195	200,706
Gross unrealized gains	389	1,929
Gross unrealized loss	2,718	1,123
Fair Value	151,866	201,512
Public Utilities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	24,898	20,215
Gross unrealized gains	19	127
Gross unrealized loss	775	85
Fair Value	24,142	20,257
Corporate Securities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	296,009	287,025
Gross unrealized gains	197	1,746
Gross unrealized loss	6,610	1,209
Fair Value	289,596	287,562
Mortgage-backed securities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	211,288	143,982
Gross unrealized gains	0	235
Gross unrealized loss	6,298	952
Fair Value	204,990	143,265
Asset-backed Securities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	59,145	14,902
Gross unrealized gains	5	23
Gross unrealized loss	252	20
Fair Value	58,898	14,905
Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	1,285	755
Gross unrealized gains	3	11
Gross unrealized loss	85	74
Fair Value	1,203	692
Fixed Maturities
Schedule of Available-for-sale Securities
Cost or adjusted/amortized cost	854,640	763,434
Gross unrealized gains	613	4,125
Gross unrealized loss	18,863	4,704
Fair Value	836,390	762,855
Mutual Fund
Schedule of Available-for-sale Securities
Equity securities cost	44,589	29,079
Equity securities unrealized gain	6,506	2,845
Equity securities unrealized loss	0	0
Equity securities fair value	51,095	31,924
Public Utilities
Schedule of Available-for-sale Securities
Equity securities cost	2,045	1,343
Equity securities unrealized gain	331	359
Equity securities unrealized loss	19	0
Equity securities fair value	2,357	1,702
Common Stock
Schedule of Available-for-sale Securities
Equity securities cost	27,016	18,856
Equity securities unrealized gain	10,893	9,093
Equity securities unrealized loss	341	47
Equity securities fair value	37,568	27,902
Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Equity securities cost	2,098	1,718
Equity securities unrealized gain	8	53
Equity securities unrealized loss	34	4
Equity securities fair value	2,072	1,767
Equity Securities
Schedule of Available-for-sale Securities
Equity securities cost	75,748	50,996
Equity securities unrealized gain	17,738	12,350
Equity securities unrealized loss	394	51
Equity securities fair value	$ 93,092	$ 63,295

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

Name:	us-gaap_EquitySecuritiesFvNi
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

Name:	us-gaap_EquitySecuritiesFvNiCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

+ Details

Name:	us-gaap_EquitySecuritiesFvNiUnrealizedGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized loss on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

+ Details

Name:	us-gaap_EquitySecuritiesFvNiUnrealizedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_PublicUtilityBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AllOtherCorporateBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_RedeemablePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MutualFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_PublicUtilityEquitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_NonredeemablePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: