Stockholders' Equity (Summary of Warrants Outstanding) (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	8,304,032
Exercise Price | $ / shares	$ 2.84
Exercise Price 70.00 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	9,205
Exercise Price | $ / shares	$ 70.00
Exercise Price 82.50 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	8,640
Exercise Price | $ / shares	$ 82.50
Warrant Expiration Date	Dec. 23, 2018
Exercise Price 107.50 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	41,872
Exercise Price | $ / shares	$ 107.50
Warrant Expiration Date	Mar. 16, 2020
Exercise Price 40.50 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	31,519
Exercise Price | $ / shares	$ 40.50
Warrant Expiration Date	Mar. 31, 2021
Exercise Price 120.00 I [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	8,492
Exercise Price | $ / shares	$ 120.00
Warrant Expiration Date	Dec. 31, 2018
Exercise Price 120.00 II [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	8,492
Exercise Price | $ / shares	$ 120.00
Warrant Expiration Date	Mar. 01, 2019
Exercise Price 22.50 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	106,381
Exercise Price | $ / shares	$ 22.50
Warrant Expiration Date	Jun. 03, 2021
Exercise Price 0.57 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	168,498
Exercise Price | $ / shares	$ 0.57
Warrant Expiration Date	Nov. 22, 2021
Exercise Price 1.50 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	7,920,933
Exercise Price | $ / shares	$ 1.50
Warrant Expiration Date	May 10, 2022
Excluding Pre-Funded Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants	8,304,032
Minimum [Member] | Exercise Price 70.00 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant Expiration Date	Apr. 12, 2018
Maximum [Member] | Exercise Price 70.00 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant Expiration Date	Jul. 15, 2018