XML 43 R54.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Revenue - Contract assets and liabilities (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Revenue.      
Balance, beginning of the period $ 22,584 $ 18,145 $ 11,009
Deferral of revenue 24,403 17,284 16,658
Recognition of deferred revenue (17,736) (12,845) (9,522)
Balance, ending of the period $ 29,251 $ 22,584 $ 18,145