Equity Financings (Details) - USD ($)	1 Months Ended			7 Months Ended	9 Months Ended
	May 31, 2015	Apr. 30, 2015	May 31, 2014	Apr. 30, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Equity Financings
Shares sold (in shares)	8,337,500
Share price (in dollars per share)	$ 19.00
Aggregate sales proceeds from issue and sell of shares of common stock under sales agreement with Stifel	$ 148,400,000				$ 0		$ 64,503,000
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
ATM 2015
Equity Financings
Aggregate stock sold pursuant to the sales agreement (in shares)					0	500,000
Aggregate receivable from sale of common stock under sales agreement with Stifel						$ 9,300,000
Maximum
Equity Financings
Aggregate sales proceeds from issue and sell of shares of common stock under sales agreement with Stifel		$ 75,000,000	$ 75,000,000