Equity Transactions - Additional Information (Details) - USD ($) |
1 Months Ended | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|---|
Mar. 31, 2018 |
Jan. 31, 2018 |
Jul. 31, 2017 |
Sep. 30, 2018 |
Sep. 30, 2018 |
|
| Stockholders Equity [Line Items] | |||||
| Net proceeds from sale of common stock | $ 270,969,000 | ||||
| ATM Sales Agreement | |||||
| Stockholders Equity [Line Items] | |||||
| Common stock shares sold | 205,202 | 445,619 | |||
| Net proceeds from sale of common stock | $ 15,900,000 | $ 27,600,000 | |||
| ATM Sales Agreement | Maximum | |||||
| Stockholders Equity [Line Items] | |||||
| Option to sell common stock for cash | $ 150,000,000 | ||||
| Amended ATM Sales Agreement | |||||
| Stockholders Equity [Line Items] | |||||
| Remaining option to sell common stock for cash | $ 72,600,000 | ||||
| Underwritten Public Offering | |||||
| Stockholders Equity [Line Items] | |||||
| Common stock shares sold | 5,043,860 | ||||
| Net proceeds from sale of common stock | $ 271,000,000 | ||||
| Shares purchased by underwriters | 657,895 | ||||
| Public offering price | $ 57.00 | ||||