Note 3 - Cash and Cash Equivalents (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017	Jan. 01, 2016	Dec. 31, 2015
Average Reserve Balances Required to be Maintained with Federal Bank	$ 5,400	$ 7,500
Average Excess Balances Maintained With Federal Reserve Bank	258,600	359,500
Margin Deposit Assets	1,800
Payments for (Proceeds from) Short-term Investments, Total	(5,000)
Payments to Acquire Businesses, Net of Cash Acquired, Total		1,392
Net Cash Provided by (Used in) Investing Activities, Total	(1,134,327)	(903,987)	(853,492)
Cash and Cash Equivalents, Period Increase (Decrease), Total	65,489	(650,283)	468,074
Cash and Cash Equivalents, at Carrying Value, Ending Balance	$ 600,290	534,801	1,185,084			$ 717,010
Previously Reported [Member]
Payments for (Proceeds from) Short-term Investments, Total		796,300	1,300,000
Payments to Acquire Businesses, Net of Cash Acquired, Total		118,400
Net Cash Provided by (Used in) Investing Activities, Total		224,700
Cash and Cash Equivalents, Period Increase (Decrease), Total		29,000	37,900
Cash and Cash Equivalents, at Carrying Value, Ending Balance		$ 247,100	$ 218,000	$ 218,000	$ 180,100