Consolidated Balance Sheets (Parenthetical) $ in Thousands, shares in Millions	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 £ / shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2017 £ / shares
Allowances for doubtful accounts	$ 9,077		$ 10,230
Reserves for inventories	59,097		69,459
Accumulated depreciation of property, plant and equipment	384,942		367,954
Accumulated amortization of intangible assets	$ 1,807,077		$ 1,599,573
Ordinary Shares
Common stock, nominal value | £ / shares		£ 0.01		£ 0.01
Common stock, shares issued | shares	181.8		185.2
Common stock, shares outstanding | shares	181.8		185.2