Equity - Issuance of Common Stock (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Issuance of Common Stock
Net proceeds from issuance of common shares		$ 0	$ 704,938
Common stock
Issuance of Common Stock
Shares issued	11,850,000
Underwriting discounts and offering costs	$ 29,800
Net proceeds from issuance of common shares	$ 704,900