Redeemable Preferred Shares - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Jan. 23, 2018	Dec. 15, 2010	Jan. 31, 2009	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2010	Jan. 22, 2018
Class of Stock [Line Items]
Par value (in USD per share)				$ 0.01	$ 0.01
Preferred shares authorized converted (in shares)	375,000						375,000
Shares authorized (in shares)				375,000	375,000
Par value (in USD per share)				$ 0.01	$ 0.01
Shares issued (in shares)				0	375,000
Shares authorized (in shares)				1,000	1,000
IPO - Shares From Goldman
Class of Stock [Line Items]
Number of shares issued (in shares)	5,163,716
Goldman | Common Stock
Class of Stock [Line Items]
Shares converted (in shares)	28,808,224
CMHI | Common Stock
Class of Stock [Line Items]
Shares converted (in shares)	4,432,034
China Merchants Holdings International Company and The Goldman Sachs Group Inc. [Member]
Class of Stock [Line Items]
Payment of accrued and unpaid dividends	$ 1,800
Series A Preferred Shares
Class of Stock [Line Items]
Number of shares issued (in shares)			125
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%
Series B Preferred Shares
Class of Stock [Line Items]
Number of shares issued (in shares)		375,000
Proceeds from issuance of shares		$ 368,500
Shares authorized (in shares)							375,000
Par value (in USD per share)							$ 0.01
Number of common shares issuable per preferred share converted (in shares)					88
Number of common shares issuable for aggregate preferred share converted (in shares)					33,240,000
Shares issued (in shares)					375,000
Liquidation value (in USD per share)								$ 1,000
Fixed dividend rate								5.00%
Payment of accrued and unpaid dividends	$ 1,200			$ 1,817	$ 28,436	$ 28,436
Series B Preferred Shares | Common Stock
Class of Stock [Line Items]
Shares converted (in shares)				33,240,258
Series B Preferred Shares | Goldman
Class of Stock [Line Items]
Number of shares issued (in shares)		325,000
Series B Preferred Shares | CMHI
Class of Stock [Line Items]
Number of shares issued (in shares)		50,000					50,000
Series C Preferred Shares
Class of Stock [Line Items]
Shares authorized (in shares)	375,000
Minimum | Series B Preferred Shares
Class of Stock [Line Items]
Participation dividend rate								2.50%