Capital Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Capitalization Equity [Line Items]
Aggregate offering price of common stock	$ 18	$ 18
Issued and sold common stock shares	183,123,000	180,536,000
Proceeds from issuance of common stock, net of issuance costs	$ 21,641
ATM Program
Schedule Of Capitalization Equity [Line Items]
Proceeds from issuance of common stock, net of issuance costs	131,200
Payments for stock issuance costs, commissions	1,700
ATM Program | Maximum
Schedule Of Capitalization Equity [Line Items]
Aggregate offering price of common stock	$ 250,000
ATM Program | Common Stock
Schedule Of Capitalization Equity [Line Items]
Issued and sold common stock shares	6,700,000
Weighted average price per share	$ 19.92