Equity, Earnings Per Share ("EPS") (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic
Net income attributable to common stockholders	$ 26,189	$ 15,614
Weighted average shares outstanding (in shares)	61,842,336	51,461,156
Net income per common share (in dollars per share)	$ 0.42	$ 0.30
Diluted
Net income attributable to noncontrolling interest	$ 8,991	$ 6,442
Net income attributable to common stockholders and noncontrolling interest	$ 35,180	$ 22,056
Weighted average shares outstanding (in shares)	61,842,336	51,461,156
Dilutive effect of OP units (in shares)	21,230,769	21,230,769
Dilutive effect of restricted stock units (in shares)	1,261,382	1,038,143
Dilutive effect of convertible notes (in shares)	365,248
Weighted average shares outstanding ( in shares)	84,699,735	73,730,068
Net income per common share (in dollars per share)	$ 0.42	$ 0.30
Chief executive officer | Performance
Diluted
Vesting period (in years)	4 years		4 years	4 years	4 years