Fair Value Measurements (Narratives) (Details) - USD ($)	3 Months Ended	6 Months Ended		12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2015	Jun. 30, 2017
Level 1 Investments
Assets
Sale of non-marketable equity investment in shares market value		$ 1,100,000
Level 1 Investments | UK Stock Exchange
Assets
Shares received for sale of non-marketable equity investment	41,685
Level 2 Investments
Assets
Transfers of assets between Level 1 and Level 2		0			$ 0
Transfers of Liabilities between Level 1 and Level 2		0			0
Long-term debt, fair value		$ 185,000,000			$ 93,700,000
Level 3
Assets
Shares received for sale of non-marketable equity investment	41,685
Sale of non-marketable equity investment in shares market value	$ 900,000
Purchases of non-marketable equity investment				$ 3,000,000
Consideration from sale of non-marketable equity investment	6,800,000
Consideration from sale of non-marketable equity investment in cash	5,400,000
Consideration from sale of non-marketable equity investment	5,800,000
Sale of non-marketable equity investment in cash	4,900,000
Remaining consideration from non-marketable securities in cash	500,000
Remaining consideration from non-marketable securities in shares	$ 500,000
Escrow period		18 months
Transfers of assets between Level 2 and Level 3		$ 0	$ 0
Transfers of liabilities between Level 2 and Level 3		0	0
Intangible asset and goodwill impairment		0	$ 0
Level 3 | Common Stock
Assets
Consideration in shares for sale of non-marketable investment	65,937
Consideration from sale of non-marketable equity investment in shares market value	$ 1,400,000
Level 3 | Other Income (Expense), Net
Assets
Gain on investments		$ 3,800,000