Common Stock and Other Equity Related Transactions - ATM Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock
Shares in common stock sold (in shares)	1,010,472	1,722,282	2,760,034
Total gross proceeds	$ 59,319	$ 78,755	$ 120,698
Commissions paid to sales agents	1,347	1,651	1,947
Private Placement
Class of Stock
Total gross proceeds	$ 59,319	$ 78,755	$ 120,698
Private Placement | Common Stock
Class of Stock
Shares in common stock sold (in shares)	1,010,472	1,722,282	2,760,034
Weighted average price (usd per share)	$ 58.71	$ 45.73	$ 43.73
Commissions paid to sales agents	$ 771	$ 1,028	$ 1,512