Equity Financings (Details) - USD ($)	1 Months Ended			3 Months Ended	6 Months Ended	7 Months Ended
	May. 31, 2015	Apr. 30, 2015	May. 31, 2014	Jun. 30, 2015	Jun. 30, 2015	Apr. 30, 2015
Equity Financings [Line Items]
Aggregate sales proceeds from issue and sell of shares of common stock under sales agreement with Stifel					$ 64,503,000
Proceeds from public offering of common stock, net of issuance costs					$ 148,439,000
Commission percentage paid		2.00%	2.00%
Aggregate stock sold pursuant to the sales agreement (in shares)						5,400,000
Aggregate receivable from sale of common stock under sales agreement with Stifel						$ 73,500,000
Underwritten public offering
Equity Financings [Line Items]
Aggregate common stock sold (in shares)	8,337,500
Share price	$ 19.00
Proceeds from public offering of common stock, net of issuance costs	$ 148,400,000
ATM 2014
Equity Financings [Line Items]
Aggregate stock sold pursuant to the sales agreement (in shares)				1,400.000
Aggregate receivable from sale of common stock under sales agreement with Stifel				$ 21,500.000
ATM 2015
Equity Financings [Line Items]
Aggregate stock sold pursuant to the sales agreement (in shares)				500,000
Aggregate receivable from sale of common stock under sales agreement with Stifel				$ 9,300,000
Maximum
Equity Financings [Line Items]
Aggregate sales proceeds from issue and sell of shares of common stock under sales agreement with Stifel		$ 75,000,000	$ 75,000,000