Significant Accounting Policies, Basic and Diluted Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income (Numerator) [Abstract]
Income available to common shareholders	$ 35,648		$ 18,931
Dilutive effect of 2 3/4 percent notes	1,047		0
Income available to common shareholders, plus assumed conversions	$ 36,695		$ 18,931
Shares (Denominator) [Abstract]
Shares used in computing basic net income per share (in shares)	119,742	117,588	119,348	117,359
Effect of Diluted Securities [Abstract]
Shares issuable upon exercise of stock options (in shares)	3,974		4,310
Shares issuable upon restricted stock award issuance (in shares)	376		399
Shares issuable related to our ESPP (in shares)	4		4
Shares issuable related to our 2 3/4 percent notes (in shares)	3,683		0
Shares used in computing diluted net income per share (in shares)	127,779	117,588	124,061	117,359
Per-Share Amount [Abstract]
Basic net income per share (in dollars per share)	$ 0.30	$ (0.10)	$ 0.16	$ (0.37)
Diluted net income per share (in dollars per share)	$ 0.29	$ (0.10)	$ 0.15	$ (0.37)
2 3/4 Percent Convertible Senior Notes [Member]
Basic and Diluted Net Income (Loss) per Share [Abstract]
Interest rate on convertible senior notes	2.75%	2.75%	2.75%	2.75%	2.75%
1 Percent Convertible Senior Notes [Member]
Basic and Diluted Net Income (Loss) per Share [Abstract]
Interest rate on convertible senior notes	1.00%		1.00%		1.00%