Stockholders' Equity - Number and Cost of Employee Stock Plan Repurchases (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Repurchases related to employee stock plans (in shares)	366	352	235
Repurchases related to employee stock plans	$ 17,399	$ 22,491	$ 13,674