Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity - Additional Information (Detail)

v3.19.1
Shareholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Jun. 14, 2018
Aug. 02, 2017
Stockholders Equity [Line Items]          
Common stock value authorized under equity offering program       $ 300,000,000  
Buyback Program, authorized repurchase amount         $ 200,000,000
Stock repurchased during period, shares 0 0      
Equity Program [Member]          
Stockholders Equity [Line Items]          
Common stock shares issued under equity offering program 0   0