Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	50,000,000	50,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	77,836,170	75,914,763
Common stock, shares outstanding	77,836,170	75,914,763
General partners' capital account, units issued	662,373	662,373
General partners' capital, units outstanding	662,373	662,373
Series C cumulative redeemable perpetual preferred units [Member]
Limited partners' capital, common units issued	8,050,000	8,050,000
Limited partners' capital, common units outstanding	8,050,000	8,050,000
Limited partners' common units [Member]
Limited partners' capital, common units issued	77,173,797	75,252,390
Limited partners' capital, common units outstanding	77,173,797	75,252,390
Series C cumulative redeemable perpetual preferred stock [Member]
Preferred stock, shares issued	8,050,000	8,050,000
Preferred stock, shares outstanding	8,050,000	8,050,000