Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Numerator used in basic and diluted EPS:
Income from continuing operations	$ 109,730	$ 96,373
(Loss) income from discontinued operations	(17,091)	2,313
Net income	$ 92,639	$ 98,686	$ 507,577
Denominator:
Weighted average number of common shares used in basic EPS	168,453,750	158,087,919
Effect of dilutive shares:
Potential common shares issuable from stock options and stock awards	3,027,134	3,393,294
Weighted average number of common shares and dilutive potential common shares used in diluted EPS	171,480,884	161,481,213