Issuance of Common Stock (Details) - USD ($) $ in Thousands			12 Months Ended
	Jul. 30, 2018	Mar. 28, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock shares issued (in shares)	4,025,000	5,175,000	54,893,000	50,248,000
Proceeds from issuance of common stock	$ 205,000	$ 136,600	$ 214,993	$ 143,810	$ 5,271
Underwriting discounts and commissions	12,000	8,800
Other direct costs incurred	$ 366	$ 816	$ 366	$ 816	$ 0