Stockholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended
	May 06, 2013	Jun. 30, 2013	Dec. 31, 2012	May 29, 2013 Class A Common Stock [Member]	Jun. 30, 2013 Class A Common Stock [Member]	May 06, 2013 Class A Common Stock [Member]
Increase in stockholders' equity		$ 639,200,000
Stockholders' Equity		712,689,000	73,444,000
Total stock, shares authorized		200,000,000
Common stock, shares authorized		100,000,000	100,000,000
Preferred stock, shares authorized		100,000,000
Common stock, shares outstanding		28,802,000	2,927,000			2,926,651
Reverse stock split ratio	0.1				0.1
Description reverse stock split					On April 26, 2013, our board of directors approved a one-for-ten reverse stock split of our class A common stock which we effected on May 6, 2013.
Reclassification of common stock to additional paid-in-capital					263,000
Additional shares issued				25,875,000
Additional shares, purchase price				$ 25.50
Issuance of additional shares, net proceeds after underwriter discounts and other offering expenses				$ 633,800,000
Common stock and stock units, shares issued and outstanding		28,894,475