Marketable Investment Securities (Details Textual) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Proceeds from Sale and Maturity of Marketable Securities	$ 4.7	$ 12.3

The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

No definition available.

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