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Sale of Additional Common Stock (Details) - USD ($)		1 Months Ended		12 Months Ended
	Sep. 19, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Proceeds from sale of common stock				$ 119,269,000	$ 115,204,000
Common Stock
Sale of common stock		5,272,750	8,625,000	5,272,750	8,625,000
Proceeds from sale of common stock		$ 119,300,000	$ 115,200,000	$ 53,000	$ 86,000
Piper Jaffray | Common Stock | Maximum
Aggregate value of stock sold	$ 40,000,000

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-Publisher FASB
-Name Accounting Standards Codification
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