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Share-Based Payments - Stock Option Plan 2015 (Details) - Stock Option Plan 2015 - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 21, 2017
Feb. 07, 2017
Mar. 31, 2017
Aug. 25, 2016
Sep. 23, 2015
Apr. 02, 2015
Share-Based Payments            
Number of awards that can be granted       346,235 177,499 95,000
Exercise period     10 years      
Vested option rights outstanding     $ 4,214      
Weighted average exercise price in $ per share            
Outstanding balance at beginning of year (in dollars per share)     $ 78.25      
Granted (in dollars per share) $ 110.00 $ 85.00 85.51      
Forfeited (in dollars per share)     88.00      
Outstanding balance at end of year (in dollars per share)     80.65      
Vested and exercisable balance at end of year (in dollars per share)     $ 77.12      
Options            
Outstanding at beginning of year (in shares)     179,436      
Granted (in shares)     102,560      
Forfeited (in shares)     (9,257)      
Outstanding at end of year (in shares)     272,739      
Vested and exercisable at end of year (in shares)     62,805      
Aggregate Intrinsic value            
Outstanding at end of year (in dollars)     $ 12,255      
Vested and exercisable at end of year (in dollars)     $ 3,926      
Options            
Share-Based Payments            
Vesting period     4 years      
Options | First year            
Share-Based Payments            
Vesting period     1 year      
Percentage that vests during the period     25.00%      
Options | Second, third and fourth years            
Share-Based Payments            
Vesting period     4 years      
Percentage that vests during the period     75.00%      
Monthly vesting percentage     2.083%