Significant Accounting Policies - At The Market Program - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2016
June 2014 Equity Distribution Agreement [Member]
Stock Issued Under At the Market Program		2,528,416
Net Proceeds Received From Share Issuances Under At The Market Program		$ 34,200,000
Total value of Common Stock to be issued under Equity Distribution Agreement		$ 35,000,000
Equity Distribution Agreement Date		June 17, 2014
September 2014 Equity Dsitribution Agreement [Member]
Stock Issued Under At the Market Program		5,087,646
Net Proceeds Received From Share Issuances Under At The Market Program		$ 69,100,000
Total value of Common Stock to be issued under Equity Distribution Agreement		$ 75,000,000
Equity Distribution Agreement Date		September 3, 2014
March 2015 Equity Distribution Agreement [Member]
Stock Issued Under At the Market Program	6,221,102
Net Proceeds Received From Share Issuances Under At The Market Program	$ 83,100,000
Total value of Common Stock to be issued under Equity Distribution Agreement			$ 100,000,000
Equity Distribution Agreement Date	March 2, 2015