Quarterly report pursuant to Section 13 or 15(d)

Changes in unearned revenue (Details)

v3.19.2
Changes in unearned revenue (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Unearned Revenue      
Balance at beginning of year $ 127,075 $ 117,614 $ 117,614
Deferral of unearned revenue 100,188 95,948 166,053
Recognition of unearned revenue (80,496) (78,290) (156,592)
Balance at end of period $ 146,767 $ 135,272 $ 127,075