Recent Accounting Pronouncements - Summary of Adjustments to Accounts on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	[1]
ASSETS
Accounts receivable, net		$ 363,566		$ 261,365
Deferred tax assets		425,380		399,095
Total assets		4,624,679		4,633,125
Equity:
Accumulated deficit		(1,677,855)		(1,637,548)
Total liabilities and stockholders' equity		$ 4,624,679		$ 4,633,125
ASC 606
ASSETS
Accounts receivable, net			$ 287,377
Deferred tax assets			393,131
Total assets			4,653,173
Equity:
Accumulated deficit			(1,617,500)
Total liabilities and stockholders' equity			4,653,173
Adjustments | ASC 606 | Tax Provision
ASSETS
Accounts receivable, net	[2]		0
Deferred tax assets	[2]		(5,964)
Total assets	[2]		(5,964)
Equity:
Accumulated deficit	[2]		(5,964)
Total liabilities and stockholders' equity	[2]		(5,964)
Adjustments | ASC 606 | Aldurazyme
ASSETS
Accounts receivable, net	[3]		26,012
Deferred tax assets	[3]		0
Total assets	[3]		26,012
Equity:
Accumulated deficit	[3]		26,012
Total liabilities and stockholders' equity	[3]		$ 26,012

[1] December 31, 2017 balances were derived from the audited Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017, filed with the SEC on February 26, 2018.

[2] The adoption of ASC 606 primarily resulted in an acceleration of the variable consideration components of revenue as of December 31, 2017, which in turn generated additional deferred tax liabilities that ultimately reduced the Company's net deferred tax asset position. The tax provision amount has been calculated using the Company’s estimated statutory rate.

[3] This adjustment represents management’s estimate of the variable consideration to be earned on worldwide sales of Aldurazyme by Genzyme in excess of the product transfer revenue previously recognized for Genzyme’s ending inventory at December 31, 2017. The product transfer revenue previously recognized as revenue represents the fixed amount per unit of Aldurazyme that Genzyme was required to pay the Company if the product was unsold by Genzyme.