Stockholders' Deficit - Share Repurchases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class of Stock [Line Items]
Stock repurchased during period, value	$ 12,015	$ 10,003
2019 Repurchase Program
Class of Stock [Line Items]
Stock repurchased during period (in shares)	40,817
Stock repurchased during period, value	$ 3,600
Cumulative amount of shares repurchased (in shares)	40,817
Cumulative payments for repurchase of common stock	$ 3,600
Remaining dollar value of shares that may be repurchased	$ 196,400
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