Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	900,000,000	900,000,000
Common stock, shares issued (in shares)	43,795,073	43,784,939
Common stock, shares outstanding (in shares)	43,795,073	43,784,939
Series A Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	36,000,000	36,000,000
Preferred stock, shares issued (in shares)	1,893,183	1,225,734
Preferred stock, shares outstanding (in shares)	1,890,943	1,224,712
Preferred stock, liquidation preference per share (in usd per share)	$ 25.00	$ 25.00
Series A Cumulative Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	36,000,000	36,000,000
Preferred stock, shares issued (in shares)	568,921	61,435
Preferred stock, shares outstanding (in shares)	566,176	60,592
Preferred stock, liquidation preference per share (in usd per share)	$ 25.00	$ 25.00
Series L Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	9,000,000	9,000,000
Preferred stock, shares issued (in shares)	8,080,740	8,080,740
Preferred stock, shares outstanding (in shares)	8,080,740	8,080,740
Preferred stock, liquidation preference per share (in usd per share)	$ 28.37	$ 28.37