Goodwill and Intangible Assets (Narrative) (Details) - USD ($)		3 Months Ended		12 Months Ended
	Sep. 15, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				$ 44,695,000	$ 44,695,000
Impairment of goodwill				0	$ 0	$ 0
Weighted average period to amortize acquired intangible assets					13 years
Standard Commercial P & C Business Unit [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				2,100,000
Workers Compensation Business Unit [Member] | Renewal Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
One-time payment related to divestiture of renewal rights			$ 83,000
Gain (loss) on disposition of property, plant and equipment		$ 400,000	$ 200,000
Proceeds from sale of finite-lived assets	$ 115,000
Specialty Commercial Segment [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				17,400,000
MGA Commercial Products [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				19,900,000
Excess and Umbrella Business Unit [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				7,700,000
General Aviation and Satellite Component [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				9,700,000
Personal Lines Business Unit [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill				$ 5,300,000