Note 8 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Preferred Stock, Shares Authorized (in shares)		50,000,000	50,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.01	$ 0.01
Preferred Stock, Shares Outstanding, Ending Balance (in shares)		0	0
Common Stock, Shares Authorized (in shares)		450,000,000	450,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.01	$ 0.01
Common Stock, Shares, Issued, Total (in shares)		154,958,240
Common Stock, Shares, Outstanding, Ending Balance (in shares)		144,515,658	143,942,539
Treasury Stock, Shares, Ending Balance (in shares)		10,442,582	10,111,191
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.10	$ 0.10	$ 0.40	$ 0.40
Dividends, Total		$ 15	$ 58	$ 58
Payments of Ordinary Dividends, Common Stock		15	$ 58	$ 58
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 150