Summary of Activity Related to Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill, Gross Carrying Amount Beginning Balance	$ 90,770
Goodwill associated with KMI Acquisition, Gross Carrying Amount	6,835
Goodwill, Gross Carrying Amount Ending Balance	97,605
Goodwill, Accumulated Impairment Losses Beginning Balance	(304)
Goodwill, Accumulated Impairment Losses Ending Balance	(304)
Goodwill, Net Carrying Amount Beginning Balance	90,466
Goodwill associated with KMI acquisition, Net Carrying Amount	6,835
Goodwill, Net Carrying Amount Ending Balance	$ 97,301