Significant Accounting Policies - Capital Raising (Details)	6 Months Ended
	Jun. 30, 2017 USD ($) shares
Initial Public Offering [Member]
Offering Period	February 20, 2013
Net Proceeds From Share Issuance	$ 35,400,000
Shares Issued In Capital Raising Program | shares	2,400,000
July 2016 At The Market Program [Member]
Offering Period	July 29, 2016
Gross Proceeds From Share Issuance	$ 110,000,000
Net 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
May 2017 At The Market Program [Member]
Offering Period	February 23, 2017
Gross Proceeds From Share Issuance	$ 125,000,000
Net Proceeds From Share Issuance	122,900,000
Stock To Be Issued Value Original	$ 125,000,000
Shares Issued In Capital Raising Program | shares	12,299,032