Nature of Business (Details) $ / shares in Units, $ in Thousands		1 Months Ended		9 Months Ended
	Dec. 19, 2016 item	Jun. 30, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) segment $ / shares	Sep. 30, 2016 USD ($)
Nature of Business and Basis of Presentation
Number of operating segments | segment				1
Minimum number of chemotherapies | item	2
Issuance of stock (in shares) | shares		3,920,454	5,750,000
Sale of stock, price per share | $ / shares		$ 88.00	$ 41.00	$ 88.00
Proceeds from offering | $		$ 324,600	$ 221,200	$ 545,838	$ 0
Minimum estimated number of months operating plan funded				12 months