Earnings Per Share , Calculation of Numerator and Denominator (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Numerator
Net income attributable to common stockholders	$ 24,115	$ 18,897	$ 57,583	$ 18,969	$ 18,969
Allocation to restricted stock awards	(189)	(135)	(461)		(22)
Basic earnings: Net income attributable to common stockholders after allocation	23,926	18,762	57,122		18,947
Allocation to restricted stock awards	189	135	461		22
Diluted earnings: Net income attributable to common stockholders after allocation	$ 24,115	$ 18,897	$ 57,583		$ 18,969
Denominator
Weighted average common shares outstanding	78,369	68,655	75,234	63,716	63,716
Add: dilutive stock options	2	8	2		10
Add: dilutive restricted stock	437	406	610		420
Diluted weighted average common shares and securities	78,808	69,069	75,846	64,146	64,146
Basic	$ 0.31	$ 0.27	$ 0.76	$ 0.30	$ 0.30
Diluted	$ 0.31	$ 0.27	$ 0.76	$ 0.30	$ 0.30