Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended		16 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Summary Of Significant Accounting Policies [Line Items]
Restructuring charges	$ 1,509,000	$ 1,411,000
Legal, professional and other costs incurred in response to unsolicited tender offer	0	10,065,000	45,607,000
Legal, professional and other costs paid	$ 43,107,000
Antidilutive common stock equivalents	1,144,000	461,000