Stockholders’ Equity - (Stock Redemption) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended	12 Months Ended				23 Months Ended	71 Months Ended
	Jan. 31, 2018	Jul. 31, 2017	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2018
Equity [Abstract]
Number of Shares (in shares)				412,939	1,225,365	7,854	1,769,738	303,907	3,719,803
Weighted Average Price per Share (in dollars per share)	$ 23.37			$ 23.37	$ 23.71	$ 24.17	$ 24.13	$ 24.01	$ 23.90
Shares rejected for repurchase (in shares)			600,000		5,900,000
Shares rejected for repurchase					$ 140.1
Shares rejected for repurchase, weighted average cost (in dollars per share)					$ 23.65
Percentage approved		100.00%
Treasury stock, shares, acquired (in shares)	412,939
Treasury stock, value, acquired, cost method	$ 9.7