Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest in equity method investment	20.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest in equity method investment	50.00%
Cash and Cash Equivalents [Member]
Summary Of Significant Accounting Policies [Line Items]
Balance in excess of FDIC-insured limits	$ 4.2
Short-Term Investments [Member]
Summary Of Significant Accounting Policies [Line Items]
Balance in excess of FDIC-insured limits	14.3
Original maturity period	26 weeks
Noncurrent Restricted Cash and Cash Equivalents [Member]
Summary Of Significant Accounting Policies [Line Items]
Balance in excess of FDIC-insured limits	65.6
Noncurrent Restricted Investments [Member] | CD [Member]
Summary Of Significant Accounting Policies [Line Items]
Balance in excess of FDIC-insured limits	$ 49.8
Original maturity period	No longer than approximately 26 weeks