Fair Value of Financial Instruments - Schedule of Fair Value of Cash Equivalents and Marketable Securities (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	$ 162,251,000	$ 0
Assets fair value disclosure	216,355,000	844,000
Common Equity Securities [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	39,000
Corporate Bonds [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	157,222,000
Commercial Paper [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	4,990,000
Money Market Mutual Funds [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Money market mutual funds (cash equivalents)	54,104,000	844,000
Quoted Prices in Active Markets (Level 1) [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets fair value disclosure	39,000
Quoted Prices in Active Markets (Level 1) [Member] | Common Equity Securities [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	39,000
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets fair value disclosure	216,316,000	844,000
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	157,222,000
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Available for sale securities	4,990,000
Significant Other Observable Inputs (Level 2) [Member] | Money Market Mutual Funds [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Money market mutual funds (cash equivalents)	$ 54,104,000	$ 844,000