Equity - Issuance of Common Stock (Details) - USD ($) $ in Thousands	1 Months Ended		6 Months Ended
	May 31, 2016	Apr. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Issuance of common stock
Net proceeds from issuance of common shares			$ 383,525	$ 276,430
Common stock
Issuance of common stock
Shares issued	6,500,000	5,500,000
Underwriting discounts and offering costs	$ 12,100	$ 1,400
Net proceeds from issuance of common shares	$ 383,500	$ 276,400