Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Issuance of shares of common stock pursuant to employee stock plans (in shares)	1,603,554	1,682,202	1,709,140
Purchase and retirement of common stock (in shares)	6,378,025	34,090,566	16,606,157
Dividends declared on common stock (in dollars per share)	$ 0.10	$ 0.40	$ 0.40
Public Stock Offering
Issuance of shares of common stock, net of offering costs (in shares)	129,490,000
At-the-market Offering
Issuance of shares of common stock, net of offering costs (in shares)	68,561,487