Convertible Notes, Net - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Nov. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Convertible notes, net		$ 162,460,000		$ 161,853,000
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Senior Notes, Principal amount	172,500,000
Convertible Senior Notes, Interest rate	5.25%
Maturity Date		Dec. 01, 2018
Convertible Senior Notes, Interest rate including underwriter discounts	5.87%
Convertible notes, net		162,500,000
Discount upon issuance of Convertible Notes	9,100,000	6,900,000
Description of Convertible Notes conversion		The Convertible Notes are convertible at the holders' option into shares of our class A common stock, only under specific circumstances, prior to the close of business on August 31, 2018, at the applicable conversion rate in effect on the conversion date.
Convertible Notes, assumed effective interest rate	6.50%
Convertible Senior Notes, Interest rate including amortization of discount upon issuance	7.16%
Total interest on convertible notes		2,900,000	2,900,000
Interest on convertible notes related to cash coupon		2,300,000	2,300,000
Interest on convertible notes related to amortization of discount and certain issuance costs		630,000	592,000
Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued	34.8943
Convertible Notes, debt conversion, principal amount	$ 1,000	$ 0
Debt instrument, conversion price	$ 28.66	$ 28.37