Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Allowances for accounts receivable	$ 24,400	$ 25,388
Allowances for vendor receivables	$ 4,036	$ 1,819
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	224,459,000	220,929,000
Common stock, shares outstanding	224,459,000	220,929,000