Consolidated Statements of Stockholders' Equity (Unaudited) (Parentheticals) - $ / shares	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Treasury shares withheld for payment of taxes, weighted average price per share (USD per share)	$ 58.68	$ 55.06	$ 49.75	$ 52.59	$ 52.99	$ 55.08