Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 10, 2017
Class of Stock [Line Items]
Net proceeds from issuance of common stock		$ 0	$ 219,504	$ 96,547
Value of common stock issued		$ 1,308,709	$ 1,284,274
Common stock, shares authorized		240,000,000	240,000,000
Preferred stock, shares authorized		5,000,000
Preferred stock, par value per share (in dollars per share)		$ 0.01
Underwritten Public Equity Offering | Common Stock
Class of Stock [Line Items]
Shares issued					26,450,000
Price per share issued (in dollars per share)					$ 8.65
Net proceeds from issuance of common stock	$ 220,000
ATM Program
Class of Stock [Line Items]
Net proceeds from issuance of common stock				96,500
Value of common stock issued				100,000
Payments for commissions				$ 2,300
ATM Program | Common Stock
Class of Stock [Line Items]
Shares issued				13,018,732