Equity - Common Stock Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 03, 2017	Sep. 08, 2015
Class of Stock [Line Items]
Dividends, Common Stock, Cash				$ 15,257	$ 10,885	$ 7,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.36	$ 0.26	$ 0.16
Common Class C, Non-Voting [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount							$ 5,400	$ 25,000
Repurchase of Class C Common Stock				668,000
Stock Repurchased and Retired During Period, Value	$ 19,600			$ 19,600