CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
4.75% Convertible Senior Notes Due 2015
Interest rate of debt (as a percent)			4.75%
Convertible Senior Notes 0.375 Percent Due 2018
Interest rate of debt (as a percent)	0.375%	0.375%
Convertible Senior Notes 1.25 Percent Due 2020
Interest rate of debt (as a percent)	1.25%	1.25%	1.25%