Redeemable Preferred Shares - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	9 Months Ended
	Jan. 23, 2018	Dec. 15, 2010	Jan. 31, 2009	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Series A par value (in USD per share)				$ 0.01		$ 0.01
Series B par value (in USD per share)				$ 0.01		$ 0.01
Goldman | IPO - Shares From Goldman
Class of Stock [Line Items]
Number of shares issued (in shares)	5,163,716
Series A Preferred Shares
Class of Stock [Line Items]
Number of shares issued (in shares)			125
Series A par value (in USD per share)			$ 0.01
Proceeds from issuance of shares			$ 100
Redemption price as a percentage of liquidation value			100.00%
Liquidation value (in USD per share)			$ 1,000
Dividend rate			12.50%
Payment for redemption of preferred shares	$ 100
Series B Preferred Shares
Class of Stock [Line Items]
Number of shares issued (in shares)		375,000
Proceeds from issuance of shares		$ 368,500
Series B par value (in USD per share)		$ 0.01
Payment of accrued and unpaid dividends	$ 1,800			$ 1,817	$ 14,218
Series B Preferred Shares | Goldman
Class of Stock [Line Items]
Number of shares issued (in shares)		325,000
Series B Preferred Shares | Goldman | Preferred Stock
Class of Stock [Line Items]
Shares converted (in shares)	28,808,224
Series B Preferred Shares | CMHI
Class of Stock [Line Items]
Number of shares issued (in shares)		50,000
Series B Preferred Shares | CMHI | Preferred Stock
Class of Stock [Line Items]
Shares converted (in shares)	4,432,034