Stockholders' Equity (Details) - $ / shares		3 Months Ended			9 Months Ended	12 Months Ended
	Dec. 12, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Stockholders' Equity
Preferred Stock, Shares Outstanding		4,600,000			4,600,000	4,600,000
Series A Cumulative Preferred Stock, dividend rate (as a percent)					7.25%	7.25%
Dividends Payable, Date of Record		Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Series A Cumulative Redeemable Preferred Stock
Stockholders' Equity
Preferred stock dividend declared (per share)		$ 0.4531	$ 0.4531	$ 0.4531	$ 1.3593
Common Stock
Stockholders' Equity
Common Stock dividend declared (per share)		$ 0.90	$ 0.90	$ 0.80	$ 2.60
Forecast
Stockholders' Equity
Preferred Stock, Shares Outstanding	4,600,000
Series A Cumulative Preferred Stock, dividend rate (as a percent)	7.25%
Redemption price of preferred stock (in dollars per share)	$ 25.00
Accrued and unpaid dividends (in dollars per share)	0.292014
Total cost of redemption (in dollars per share)	$ 25.292014