Stockholders' Deficit - Share Repurchases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Stock repurchased during period, value	$ 26,527	$ 111,697	$ 34,929
2019 Repurchase Program
Class of Stock [Line Items]
Stock repurchased during period (in shares)	459,899	1,237,698
Stock repurchased during period, value	$ 26,500	$ 103,300
Cumulative amount of shares repurchased (in shares)	1,697,597
Cumulative payments for repurchase of common stock	$ 129,800
Remaining dollar value of shares that may be repurchased	$ 70,200
October 2015 Share Repurchase Program
Class of Stock [Line Items]
Stock repurchased during period (in shares)		110,499
Stock repurchased during period, value		$ 8,400
Cumulative amount of shares repurchased (in shares)		1,589,995
Cumulative payments for repurchase of common stock		$ 126,200