Schedule II Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net income	$ 27,001	$ (28,012)	$ 7,257	$ 3,899	$ (10,517)	$ 3,423	$ 9,841	$ 2,951	$ 10,145	$ 5,698	$ 27,358
Depreciation and amortization									37,532	11,713	3,328
Gain (Loss) on Sale of Securities, Net									(67)	(547)	(827)
Increase (Decrease) in Deferred Income Taxes									(8,584)	2,210	2,305
Share-based Compensation									2,613	1,947	1,974
Increase (Decrease) in Accrued Investment Income Receivable									(531)	(172)	(676)
Increase (Decrease) in Other Operating Assets									4,051	(11,006)	(3,897)
Accounts payable									15,905	8,005	(1,837)
Increase (Decrease) in Other Operating Liabilities									28,739	12,300	4,612
Net Cash Provided by (Used in) Operating Activities									14,309	65,747	98,319
Proceeds from sales and maturities of investments available for sale									128,329	187,522	199,575
Payments to Acquire Property, Plant, and Equipment									(5,237)	(3,149)	(10,916)
Net Cash Provided by (Used in) Investing Activities									(7,344)	(49,757)	(67,015)
Payments Related to Tax Withholding for Share-based Compensation									(287)	(270)	(185)
Repayments of Long-term Debt									40,075	1,379	3,422
Payments of Debt Issuance Costs									3,264	596	0
Payments of Dividends									8,991	4,974	4,302
Net Cash Provided by (Used in) Financing Activities									118,622	49,912	(7,909)
Cash and Cash Equivalents, Period Increase (Decrease)									125,587	65,902	23,395
Cash and Cash Equivalents, at Carrying Value	276,275				150,688				276,275	150,688	84,786	$ 61,391
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net income									10,145	5,698	27,358
Depreciation and amortization									1,208	682	74
Gain (Loss) on Sale of Securities, Net									0	14	(951)
Increase (Decrease) in Deferred Income Taxes									(777)	382	126
Share-based Compensation									2,613	1,947	1,974
Increase (Decrease) in Accrued Investment Income Receivable									0	3	(3)
Increase (Decrease) in Other Operating Assets									359	(22,553)	450
Accounts payable									447
Increase (Decrease) in Notes Payable, Related Parties									11,597	5,874	2,557
Increase (Decrease) in Other Operating Liabilities									(1,905)	1,969	918
Net Cash Provided by (Used in) Operating Activities									23,687	(5,984)	32,503
Proceeds from sales and maturities of investments available for sale									0	34,551	19,633
Payments to Acquire Investments									(26,584)	(70)	(53,212)
Payments to Acquire Interest in Subsidiaries and Affiliates									(23,283)	(68,563)	16,276
Payments to Acquire Property, Plant, and Equipment									(449)	(1,797)	(3,255)
Net Cash Provided by (Used in) Investing Activities									(50,316)	(35,879)	(20,558)
Payments Related to Tax Withholding for Share-based Compensation									(287)	(270)	(185)
Repayments of Long-term Debt									(38,897)
Payments of Debt Issuance Costs									(3,264)
Proceeds from Issuance of Debt									150,000	42,951	0
Payments of Dividends									8,991	4,974	4,302
Net Cash Provided by (Used in) Financing Activities									98,561	37,707	(4,487)
Cash and Cash Equivalents, Period Increase (Decrease)									71,932	(4,156)	7,458
Cash and Cash Equivalents, at Carrying Value	$ 79,331				$ 7,399				$ 79,331	$ 7,399	$ 11,555	$ 4,097