XML 38 R56.htm IDEA: XBRL DOCUMENT v3.19.3
Stockholders' Equity - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Jun. 30, 2018
Sep. 30, 2019
Dec. 31, 2018
May 01, 2018
Class of Stock [Line Items]          
Additional shares issued 266,410 213,276      
Shelf Registration [Member]          
Class of Stock [Line Items]          
Additional shares issued     0    
Common Class A [Member]          
Class of Stock [Line Items]          
Issuance of shares related to acquisition       163,137  
Common Class A [Member] | Equity Distribution Agreement [Member]          
Class of Stock [Line Items]          
Common stock, shares sold     842,412    
Common stock, shares available to be sold $ 336,668   $ 336,668    
Common Class A [Member] | Maximum [Member]          
Class of Stock [Line Items]          
Aggregate offering price of common stock issuable         $ 400,000