Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2015	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Amount paid for shares repurchased			$ 0	$ 75,697
2015 ATM Equity Program
Class of Stock [Line Items]
Maximum aggregate offering price	$ 250,000
Number of common shares sold			0	0
Aggregate offering price of remaining common shares available for sale			$ 250,000
2015 Share Repurchase Program
Class of Stock [Line Items]
Maximum authorized amount for stock repurchases	$ 250,000
Increase in authorized amount for repurchases					$ 250,000
Number of shares repurchased		6,024	0	6,024
Average repurchase price per share		$ 12.55		$ 12.55
Amount paid for shares repurchased		$ 75,697		$ 75,697
Remaining authorized repurchase amount			$ 264,057