Convertible Notes, Net - Additional Information (Detail)		1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 28, 2016 USD ($) $ / shares	Nov. 30, 2013 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Interest on convertible notes related to amortization of discount and certain issuance costs			$ 4,535,000	$ 4,053,000
Convertible notes, net			167,475,000		$ 166,762,000
Accrued interest payable			11,673,000		9,049,000
Deferred financing costs			15,974,000		15,272,000
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Senior Notes, Principal amount		$ 172,500,000	$ 172,500,000		$ 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%
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.
Discount upon issuance of Convertible Notes		$ 9,100,000	$ 4,800,000		$ 5,500,000
Debt issuance costs		$ 4,100,000
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			3,000,000	3,000,000
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			713,000	$ 670,000
Accrued interest payable			3,000,000		755,000
Deferred financing costs			$ 180,000		$ 206,000
5.25% Convertible Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price | $ / shares			$ 30.96
5.25% Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent	35.7236	34.8943
Convertible Notes, debt conversion, principal amount	$ 1,000	$ 1,000
Debt instrument, conversion price | $ / shares	$ 27.99	$ 28.66