Related Parties - Transactions with Agile Sports Technologies, Inc. (doing business as "Hudl") (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 07, 2017	Mar. 17, 2015
Agile Sports Technologies, Inc. [Member]
Related Party Transaction [Line Items]
Cost method investment					$ 40,500
Ownership percentage, cost method investment	19.70%
Agile Sports Technologies, Inc. [Member] | Preferred Stock Investment In Hudl [Member]
Related Party Transaction [Line Items]
Cost method investment				$ 10,400
Assurity Life Insurance Company [Member] | Payment For Insurance Premiums [Member]
Related Party Transaction [Line Items]
Transaction with related party	$ 1,500
Assurity Life Insurance Company [Member] | Reinsurance Premiums Paid For By Related Party [Member]
Related Party Transaction [Line Items]
Transaction with related party	1,400
Assurity Life Insurance Company [Member] | Annual Insurance Claim Refund [Member]
Related Party Transaction [Line Items]
Transaction with related party	10
Assurity Life Insurance Company [Member] | Remitted Employee Paid Insurance Premiums [Member]
Related Party Transaction [Line Items]
Transaction with related party	$ 181	$ 166	$ 116
Mr. Dunlap [Member] | Agile Sports Technologies, Inc. [Member]
Related Party Transaction [Line Items]
Ownership percentage, related party	3.40%
Subsidiaries [Member]
Related Party Transaction [Line Items]
Payment for insurance claims	$ 700