Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Recorded Basis	$ 10,597	$ 5,909
Recorded Basis	32,033	19,787
Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	10,689	5,953
Gross Unrealized Losses	(92)	(44)
Recorded Basis	10,597	5,909
Corporate Bonds [Member] | Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	6,285	1,879
Gross Unrealized Losses	(63)	(27)
Recorded Basis	6,222	1,852
Fair Value Category	2
Municipal Bonds [Member] | Long-Term Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	4,404	4,074
Gross Unrealized Losses	(29)	(17)
Recorded Basis	4,375	4,057
Fair Value Category	2
Current Available-for-Sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	32,045	19,800
Gross Unrealized Losses	(12)	(13)
Recorded Basis	32,033	19,787
Current Available-for-Sale [Member] | Variable Rate Demand Notes (VRDN) [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	22,000	10,000
Gross Unrealized Losses	0	0
Recorded Basis	22,000	10,000
Fair Value Category	2
Current Available-for-Sale [Member] | Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	10,045	9,800
Gross Unrealized Losses	(12)	(13)
Recorded Basis	$ 10,033	$ 9,787
Fair Value Category	2