Fair Value - Fair Value Measurement of Financial Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value disclosure	$ 175,746
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	167,121
Other assets	8,625
(Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value disclosure	175,746
(Level 1) Quoted Prices in Active Markets for Identical Assets [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	167,121
Other assets	8,625
(Level 2) Significant Other Observable Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value disclosure	0
(Level 2) Significant Other Observable Inputs [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Other assets	0
(Level 3) Significant Unobservable Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value disclosure	0
(Level 3) Significant Unobservable Inputs [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Other assets	$ 0