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Cash Dividend (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]    
Cash dividend declaration date Mar. 06, 2019 Dec. 10, 2018
Cash dividend record date Mar. 27, 2019 Dec. 27, 2018
Cash dividend distributed date Apr. 10, 2019 Jan. 10, 2019
Cash dividend per share $ 0.020 $ 0.020
Cash dividend paid $ 580 $ 581