Business Segments and Geographic Areas - Summary of Company's Revenues from External Customers and Long-Lived Assets, by Geographical Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues	$ 210,760	$ 216,294	$ 212,145	$ 197,071	$ 281,227	$ 200,762	$ 195,543	$ 178,968	$ 836,270	$ 856,500	$ 646,686
Total Long-Lived Assets	877,818				785,472				877,818	785,472
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues									747,063	699,298	618,270
Total Long-Lived Assets	846,377				752,936				846,377	752,936
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues									89,207	157,202	28,416
Total Long-Lived Assets	$ 31,441				$ 32,536				$ 31,441	$ 32,536