Note 4 - Cash, Cash Equivalents and Restricted Cash (Details Textual) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jan. 01, 2018
Average Reserve Balances Required to be Maintained with Federal Bank	$ 161		$ 5,400
Margin Deposit Assets	6,900		1,800
Restricted Cash, Total	31,400		$ 7,800
Payments for (Proceeds from) Short-term Investments, Total	(0)	$ (5,000)
Net Cash Provided by (Used in) Investing Activities, Total	$ (814,030)	(674,653)
Previously Reported [Member]
Payments for (Proceeds from) Short-term Investments, Total		0
Net Cash Provided by (Used in) Investing Activities, Total		(679,700)
Cash and Cash Equivalents, Period Increase (Decrease), Total		$ (135,700)
Cash and Cash Equivalents, at Carrying Value, Ending Balance				$ 539,800

Average reserve balances required to be maintained with federal bank.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

+ References

No definition available.

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- Definition

The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

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- Definition

Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The net amount paid (received) by the reporting entity through acquisition or sale and maturities of short-term investments with an original maturity that is three months or less which qualify for treatment as an investing activity based on management's intention and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

+ References

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- Definition

Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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