Share-Based Compensation - Restricted Stock (Details) - Participating securities shares in Thousands	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Shares of Unvested Restricted Stock
Unvested restricted stock, beginning balance (in shares) | shares	11,858
Granted (in shares) | shares	5,364
Vested (in shares) | shares	(4,973)
Forfeited (in shares) | shares	(1,027)
Unvested restricted stock, ending balance (in shares) | shares	11,222
Weighted Average Grant Date Fair Value Per Share
Unvested restricted stock, beginning balance (in dollars per share) | $ / shares	$ 4.43
Granted (in dollars per share) | $ / shares	2.85
Vested (in dollars per share) | $ / shares	4.36
Forfeited (in dollars per share) | $ / shares	3.67
Unvested restricted stock, ending balance (in dollars per share) | $ / shares	$ 3.78