Stockholders' Deficit - Share Repurchases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Stock repurchased during period, value	$ 35,341	$ 10,000	$ 47,356	$ 20,003
2019 Repurchase Program
Class of Stock [Line Items]
Stock repurchased during period (in shares)	392,132		432,949
Stock repurchased during period, value	$ 35,300		$ 39,000
Cumulative amount of shares repurchased (in shares)	432,949		432,949
Cumulative payments for repurchase of common stock	$ 39,000		$ 39,000
Remaining dollar value of shares that may be repurchased	$ 161,000		$ 161,000
October 2015 Share Repurchase Program
Class of Stock [Line Items]
Stock repurchased during period (in shares)	0		110,499
Stock repurchased during period, value	$ 0		$ 8,400
Cumulative amount of shares repurchased (in shares)	1,589,995		1,589,995
Cumulative payments for repurchase of common stock	$ 126,200		$ 126,200