Stockholders' Equity (Stock Option Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of shares
Options outstanding, beginning balance (in shares)	1,538,967	1,045,913	3,444,252
Options granted (in shares)	50,000	925,000	0
Options exercised (in shares)	(75,000)	(68,259)	(347,752)
Options forfeited (in shares)	(60,000)	(363,687)
Options expired (in shares)	(456,775)		(2,050,587)
Options outstanding, ending balance (in shares)	997,192	1,538,967	1,045,913
Options exercisable (in shares)	568,025
Weighted-Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 11.27	$ 17.89	$ 30.65
Options granted (in dollars per share)	3.67	5.64
Options exercised (in dollars per share)	1.89	17.44	15.45
Options forfeited (in dollars per share)	5.38	15.15
Options expired (in dollars per share)	15.92		39.74
Options outstanding, ending balance (in dollars per share)	9.82	$ 11.27	$ 17.89
Options exercisable (in dollars per share)	$ 16.10
Options withheld (in shares)			125,523