Issuance of Notes Payable and Warrants - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Aug. 21, 2008	Dec. 31, 2012
Issuance Of Notes Payable And Warrants [Line Items]
Principal amount of Senior Notes	$ 120,000	$ 120,000
Principal amount of Senior Notes due, year	2020
Senior Notes coupon interest	5.20%
Senior Notes effective yield		7.94%
Maximum percent of aggregate principal amount of Senior Notes owned by holder or group of affiliates for transfer		15.00%
Maximum percent of voting securities and total shares of class A common stock owned by holder or group of affiliates for warrant transfer		2.00%
Class A | Maximum
Issuance Of Notes Payable And Warrants [Line Items]
Percent of outstanding shares of common stock owned by holder or group of affiliates for warrant transfer		25.00%
Senior Notes
Issuance Of Notes Payable And Warrants [Line Items]
Event of default under the indenture Accreted Amount due and payable, percentage		33.33%
Warrant | Class A
Issuance Of Notes Payable And Warrants [Line Items]
Number of Class A Shares purchased, warrants	5,455
Class A Shares purchase price per share	$ 22.00