Common Stock and Other Equity Related Transactions (Movement during the period) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Commissions paid to sales agents	$ 1,433	$ 723
Private Placement
Class of Stock [Line Items]
Total gross proceeds	$ 78,755	$ 42,037
Private Placement | Common Stock
Class of Stock [Line Items]
Shares of Common Stock sold (shares)	861,141	484,913
Weighted average price (usd per share)	$ 91.45	$ 86.69
Commissions paid to sales agents	$ 1,028	$ 526