Shareholders’ Equity (Narrative) (Details)	1 Months Ended											3 Months Ended	4 Months Ended	12 Months Ended
	Jul. 31, 2018 USD ($) shares	Mar. 31, 2018 USD ($) $ / shares shares	Aug. 31, 2017 shares	Mar. 31, 2017 USD ($) $ / shares shares	Feb. 28, 2017 consultant shares	Jan. 31, 2017 shares	Dec. 31, 2016 shares	Sep. 30, 2016 shares	Jan. 31, 2016 shares	Dec. 31, 2014 party shares	Sep. 30, 2013 employee shares	Dec. 31, 2016 shares	Nov. 30, 2015 consultant shares	Dec. 31, 2018 USD ($) series $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Jan. 31, 2019 shares	Jul. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (in shares)														8,000,000
Preferred stock, par value (usd per share) | $ / shares														$ 0.0001
Weighted-average grant date fair values of stock options granted (in dollars per share) | $ / shares														$ 20.52	$ 23.80	$ 15.33
Unamortized share-based compensation expense | $														$ 64,500,000
Recognized weighted average period														2 years 8 months 50 days
Stock options exercised (in shares)														106,370	174,628	17,548
Intrinsic value of stock options exercised | $														$ 1,400,000	$ 3,300,000	$ 100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | $														38,000,000	12,100,000	14,500,000
Warrants granted to purchase common stock (in shares)										51,000
Warrants issued, number of third party recipients (party) | party										2
Third party share-based compensation expense | $															600,000	200,000
Share-based compensation expense | $														$ 35,151,000	$ 21,795,000	$ 14,546,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of unvested stock awards (in shares)							1,072,899					1,072,899		0	542,680	1,072,899
Vested awards (in shares)														542,680	530,219
Grant One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant vesting period										4 years
Chief Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of unvested stock awards (in shares)																		1,042,680
Accelerated shares (in shares)							500,000
Vested awards (in shares)															542,680
One-year Anniversary Date of Grant [Member] | Grant One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant vesting rights percentage										25.00%
One-year Anniversary Date of Grant [Member] | Grant Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant vesting rights percentage						100.00%			100.00%	100.00%
2013 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity plan, term											10 years
Period of share-based payment awards											4 years
Shares of common stock authorized for issuance (in shares)							4,600,000					4,600,000			8,100,000	4,600,000
Shares available for grant (in shares)														1,340,450
2013 Equity Plan [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards											1 year
2013 Equity Plan [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards			2 years		1 year
Award vesting rights, percentage					25.00%
Stock options granted (in shares)					42,000
Share-based compensation expense | $														$ 300,000	$ 400,000
Number of award recipients (consultant/employee) | consultant					3
Number of stock options (option)					2
Number of modified stock options (option)			2
2013 Equity Plan [Member] | Consultant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)													50,000
Share-based compensation expense | $																$ (100,000)
Number of award recipients (consultant/employee) | consultant													2
Performance achievement percent												75.00%
Percentage of options canceled												25.00%
2013 Equity Plan [Member] | One-year Anniversary Date of Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage											25.00%
2013 Equity Plan [Member] | Share-based Compensation Award, Tranche One [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards					3 years
2013 Equity Plan [Member] | Share-based Compensation Award, Tranche Two [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards					2 years
2018 Employee Stock Purchase Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)	750,000													717,701
Maximum number of shares per employee | $	$ 25,000
Percent of employee's annual cash compensation	10.00%
Purchase price of common stock, percent	85.00%
Share-based compensation expense | $														$ 200,000
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued (in shares)		43,056												3,910,000	3,731,000
Class Of Warrant Or Right, Exercised During The Period		83,013
Class of Warrant or Right, Outstanding														10,000
Stock options exercised (in shares)														150,000	175,000	17,000
Common Stock [Member] | Director [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued (in shares)											79,622
Common Stock [Member] | Chief Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued (in shares)											1,327,048
Common Stock [Member] | Employees [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued (in shares)											336,185
Number of award recipients (consultant/employee) | employee											3
Series C-1 Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (in shares)														11,000	11,000
Preferred stock, par value (usd per share) | $ / shares														$ 0.0001	$ 0.0001
Shares issued upon conversion, per share (in shares)														1,724
Preferred stock, shares issued (in shares)														3,906	3,906
Preferred stock, shares outstanding (in shares)														3,906	3,906
Shares reserved for future issuance (in shares)														6,735,378	6,735,378
Liquidation preference per share (in dollars per share) | $ / shares														$ 1,000
Liquidation preference | $														$ 3,906,000	$ 3,906,000
Series F Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (in shares)														10,000	10,000
Preferred stock, par value (usd per share) | $ / shares														$ 0.0001	$ 0.0001
Shares issued upon conversion, per share (in shares)														286
Preferred stock, shares issued (in shares)														2,737	2,737
Preferred stock, shares outstanding (in shares)														2,737	2,737
Shares reserved for future issuance (in shares)														782,031	782,032
Liquidation preference per share (in dollars per share) | $ / shares														$ 1,000
Liquidation preference | $														$ 2,737,000	$ 2,737,000
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant granted to purchase common stock (in shares)						25,013			17,000
Common Stock [Member] | 2013 Equity Plan [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage								25.00%
Stock options granted (in shares)								35,000
Common Stock [Member] | 2013 Equity Plan [Member] | Share-based Compensation Award, Tranche One [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards								1 year
Common Stock [Member] | 2013 Equity Plan [Member] | Share-based Compensation Award, Tranche Two [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of share-based payment awards								3 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of series (series) | series														1
Underwriting Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock to be issued and sold in underwriting agreement (in shares)		3,910,000		3,731,344
Price per share of shares sold (usd per share) | $ / shares		$ 29.50		$ 33.50
Proceeds from the underwriting agreement, including additional shares sold, gross | $		$ 115,300,000		$ 125,000,000
Proceeds from the underwriting agreement, including additional shares sold, net of cost | $		109,800,000		117,500,000
Issuance costs | $		$ 5,500,000		$ 7,500,000
Subsequent Event | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon conversion, per share (in shares)																	782,031