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Summary Of Significant Accounting Policies - Disclosure of Foreign Exchange Rates (Detail)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
U.S. Dollar [member]      
Disclosure of foreign exchange rates [line items]      
Average rate 1.1273 1.1063 1.1089
Closing rate 1.1993 1.0541 1.0887
Swiss Franc [member]      
Disclosure of foreign exchange rates [line items]      
Average rate 1.1103 1.0901 1.0669
Closing rate 1.1702 1.0739 1.0835
Czech Republic, Koruny [member]      
Disclosure of foreign exchange rates [line items]      
Average rate 26.3151 27.0342 27.2762
Closing rate 25.5349 27.0210 27.0226