Quarterly Financial Data - Results of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Quarterly Financial Data Results Of Operations [Abstract]
Revenues	$ 333,615	$ 305,498	$ 254,582	$ 248,304	$ 214,327	$ 184,710	$ 149,063	$ 138,566	$ 1,141,999	$ 686,668	$ 330,422
Operating income	122,133	150,862	113,450	117,953	86,619	72,038	60,184	58,152	504,398	276,993	152,567
Net income	$ 54,490	$ 54,499	$ 67,119	$ 51,851	$ 42,591	$ 18,314	$ 76,041	$ 16,442	$ 227,959	$ 153,388	$ 79,390