Subsequent Events (Tables)	6 Months Ended
	Jun. 30, 2018
Subsequent Events [Abstract]
Follow-on Public Offering, June 2018 [Table Text Block]	In the June 2018 follow-on public offering, the Company sold 2,090,909 shares of common stock (inclusive of 272,727 shares of common stock sold by the Company pursuant to the full exercise of the underwriters' option to purchase additional shares) at a price to the public of $33.00 per share. The Company received aggregate net proceeds of $65.9 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company.On July 18, 2018, the Company purchased an equity interest, as a limited partner, in a privately held corporation for approximately $3.0 million. The Company has a contingent commitment to purchase an additional $4.0 million of equity for eighteen months following the initial investment. In conjunction with the investment, the Company has extended a revolving line of credit with a maximum borrowing capacity of $2.5 million.
Building Purchase [Table Text Block]	n July 18, 2018, the Company purchased an equity interest, as a limited partner, in a privately held corporation for approximately $3.0 million. The Company has a contingent commitment to purchase an additional $4.0 million of equity for eighteen months following the initial investment. In conjunction with the investment, the Company has extended a revolving line of credit with a maximum borrowing capacity of $2.5 million.