Note 6 - Stockholders' Equity (Details Textual) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Nov. 06, 2016 USD ($)	Mar. 31, 2006 shares	Nov. 30, 2004 shares	Mar. 31, 2004 shares
Capital Units, Authorized		245,000,000
Common Stock, Shares Authorized	100,000,000	200,000,000	100,000,000
Preferred Stock, Shares Authorized		20,000,000
Common Stock, Voting Rights, Votes Per Share		1
Dividends, Common Stock, Total | $		$ 0	$ 0	$ 0
Proceeds from Issuance of Common Stock | $			238,945
Treasury Stock, Value, Acquired, Cost Method | $		$ 19,607	$ 4,000	$ 2,000
Common Stock, Capital Shares Reserved for Future Issuance	7,422,965	7,078,916	7,422,965
March 2004 Authorization [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased								2,000,000
The 2004-2006 Repurchase Authorization [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						5,000,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased		279,200
The 2016 Repurchase Authorization [Member]
Stock Repurchase Program, Authorized Amount | $					$ 75,000
Treasury Stock, Shares, Acquired		1,551,710
Treasury Stock Acquired, Average Cost Per Share | $ / shares		$ 12.64
Treasury Stock, Value, Acquired, Cost Method | $		$ 19,600
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $		$ 49,500
November 2004 Authorization [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased							2,000,000
Underwritten Offering [Member]
Stock Issued During Period, Shares, New Issues	17,250,000
Share Price | $ / shares	$ 14.50		$ 14.50
Proceeds from Issuance of Common Stock | $	$ 238,900
Issuance of Stock, Underwriting Discount | $	10,600
Issuance of Stock, Underwriting Expenses | $	$ 600
Common Class A [Member]
Common Stock, Shares Authorized	15,000,000	25,000,000	15,000,000
Common Stock, Voting Rights, Votes Per Share		10
Common Stock, Capital Shares Reserved for Future Issuance	1,923,144	1,703,064	1,923,144