CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Preferred stock, authorized (shares)	16,670,000
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, authorized (shares)	100,000,000	100,000,000
Common stock, issued (shares)	67,306,615	67,287,231
Common stock, outstanding (shares)	67,306,615	67,287,231
Redeemable Preferred Stock
Preferred stock, dividend rate	7.25%	7.25%
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (usd per share)	$ 25	$ 25
Preferred stock, authorized (shares)	13,409,650	5,409,650
Preferred stock, issued (shares)	5,413,665	5,409,650
Preferred stock, outstanding (shares)	5,413,665	5,409,650