Description of Business and Summary of Significant Accounting Policies (Antidilutive securities excluded from computation of earnings per share) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	11,215	10,797
Outstanding options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	357	361
Unvested restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	0	26
Unvested restricted stock unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	2,757	2,650
Employee stock purchase plan awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	122	38
Bonus and director fees to be paid in stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	734	477
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive, shares	7,245	7,245