Marketable Securities (Narratives) (Details) - USD ($)

3 Months Ended

9 Months Ended

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Sep. 30, 2016

Dec. 31, 2017

Dec. 31, 2016

Mar. 31, 2018

Mar. 31, 2017

Gain (Loss) on Investments [Line Items]

Marketable securities, realized loss, other than temporary impairments, description

The Company generally considers market value declines to be other-than-temporary if there are declines for a period longer than six months and in excess of 20% of original cost, or when other evidence indicates impairment.  We also consider the nature of the underlying investments, our intent and ability to hold the investments until their market values recover, and other market conditions in making this assessment.

Marketable Securities, Realized Gain (Loss)

$ (400)

$ 1,000

$ (200)

$ 116,000

Proceeds from Sale and Maturity of Marketable Securities

6,000,000

$ 10,000,000

$ 6,000,000

Available-for-sale Securities, Short-term Investments, Amortized Cost

5,938,000

$ 5,938,000

Proceeds for CMIC Loan [Member]

Gain (Loss) on Investments [Line Items]

Gain on sale of certain investments

$ 62,000

Scenario, Forecast [Member]

Gain (Loss) on Investments [Line Items]

Minimum decline in value of marketable securities to be called as other than temporaty impairment period

6 months

Minimum decline in value of marketable securities to be called as other than temporary impairment percent

20.00%

Proceeds from Sale and Maturity of Marketable Securities

$ 10,000,000