Consolidated Balance Sheets (Parenthetical) $ in Thousands, shares in Millions	Dec. 31, 2017 USD ($) shares	Dec. 31, 2017 £ / shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2016 £ / shares
Allowances for doubtful accounts	$ 10,230		$ 15,253
Reserves for inventories	69,459		72,596
Accumulated depreciation of property, plant and equipment	367,954		319,473
Accumulated amortization of intangible assets	$ 1,599,573		$ 1,254,360
Ordinary Shares
Common stock, nominal value | £ / shares		£ 0.01		£ 0.01
Common stock, shares issued | shares	185.2		190.1
Common stock, shares outstanding | shares	185.2		190.1