Significant Accounting Policies - Capital Raising (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) shares
Initial Public Offering [Member]
Offering Period	February 20, 2013
Proceeds From Share Issuance	$ 35,400,000
Shares Issued In Capital Raising Program | shares	2,400,000
January 2014 Follow On Offering [Member]
Offering Period	January 23, 2014
Underwriters Overallotment Period	January 29, 2014
Underwriters Overallotment Shares | shares	270,000
Proceeds From Share Issuance	$ 24,200,000
Shares Issued In Capital Raising Program | shares	1,800,000
March 2014 Follow On Offering [Member]
Offering Period	March 24, 2014
Underwriters Overallotment Period	April 11, 2014
Underwriters Overallotment Shares | shares	480,000
Proceeds From Share Issuance	$ 44,000,000
Shares Issued In Capital Raising Program | shares	3,200,000
June 2014 At The Market Program [Member]
Offering Period	June 17, 2014
Proceeds From Share Issuance	$ 34,200,000
Stock To Be Issued Value Original	$ 35,000,000
Shares Issued In Capital Raising Program | shares	2,528,416
September 2014 At The Market Program [Member]
Offering Period	September 3, 2014
Proceeds From Share Issuance	$ 69,100,000
Stock To Be Issued Value Original	$ 75,000,000
Shares Issued In Capital Raising Program | shares	5,087,646
March 2015 At The Market Program [Member]
Offering Period	March 2, 2015
Proceeds From Share Issuance	$ 83,100,000
Stock To Be Issued Value Original	$ 100,000,000
Shares Issued In Capital Raising Program | shares	6,221,102
July 2016 At The Market Program [Member]
Offering Period	July 29, 2016
Proceeds From Share Issuance	$ 108,200,000
Stock To Be Issued Value Original	$ 125,000,000
Shares Issued In Capital Raising Program | shares	10,174,992