Stockholders' Equity of the Company (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
	Aug. 08, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Shares issued, value		$ 1,007		$ 986
Common Stock of the Company [Abstract]
Common stock, shares issued (in shares)		100,746,988		98,620,333
Net proceeds from issuance of common stock (Note 6)		$ 130,744	$ 308,812
Prior At-The-Market Program [Member]
Common Stock of the Company [Abstract]
At the market stock offering aggregate gross sales price of common stock		300,000
2018 At-The-Market Program [Member]
Common Stock of the Company [Abstract]
At the market stock offering aggregate gross sales price of common stock		$ 500,000
Issuance of Equity - at the market offering [Member]
Common Stock of the Company [Abstract]
Weighted average price per common share (in dollars per share)		$ 73.64
Common Stock [Member] | 2018 At-The-Market Program [Member]
Common Stock of the Company [Abstract]
At the market stock offering remaining amount available for issuance		$ 466,200
Common stock, shares issued (in shares)		447,466
Forward equity sale
Class of Stock [Line Items]
Shares issued, value	$ 360,500
Price per share (in dollars per share)	$ 72.10
Forward equity sale | Common Stock [Member]
Class of Stock [Line Items]
Number of shares issued (in shares)	5,000,000