Acquisitions - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		0 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Mar. 07, 2014 Ionia [Member]	Jun. 30, 2014 Ionia [Member]	Jun. 30, 2014 Ionia [Member]	Mar. 07, 2014 Ionia [Member]
Business Acquisition [Line Items]
Initial cash payment					$ 7,500,000
Contingent payments								4,000,000
Maturity period for contingent payment							2 years
Operating revenues	54,975,000	40,670,000	103,995,000	78,107,000		600,000	800,000
Operating expenses	46,796,000	36,017,000	88,098,000	75,675,000		1,600,000	2,100,000
Range of contingent payments, Minimum						0	0
Range of contingent payments, Maximum						4,000,000	4,000,000
Acquisition-related costs						100,000	100,000
Increase in goodwill						700,000
Deferred tax liability, intangible assets						$ 700,000	$ 700,000