Cash, Cash Equivalents, and Investments - Summary of Cash, Cash Equivalents and Held-to-Maturity Investments by Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	$ 91,611	$ 118,305
Gross Unrealized Gains	17	11
Gross Unrealized Losses	(15)	(79)
Fair Value	91,613	118,237
Cash and Cash Equivalents	37,306	59,526
Short-term investments	49,711	50,254
Long-term investments	4,594	8,525
Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	34,824	38,795
Gross Unrealized Gains	7	0
Gross Unrealized Losses	(15)	(70)
Fair Value	34,816	38,725
Cash and Cash Equivalents	1,025	2,389
Short-term investments	29,975	35,677
Long-term investments	3,824	729
Fair Value, Inputs, Level 2
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	21,336	22,373
Gross Unrealized Gains	10	11
Gross Unrealized Losses	0	(9)
Fair Value	21,346	22,375
Cash and Cash Equivalents	830	0
Short-term investments	19,736	14,577
Long-term investments	770	7,796
Fair Value, Inputs, Level 2 | State and Municipal Obligations
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	19,201	19,002
Gross Unrealized Gains	10	11
Gross Unrealized Losses	0	(9)
Fair Value	19,211	19,004
Cash and Cash Equivalents	830	0
Short-term investments	17,601	12,000
Long-term investments	770	7,002
Fair Value, Inputs, Level 2 | Certificates of Deposit
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	2,135	3,371
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	2,135	3,371
Cash and Cash Equivalents	0	0
Short-term investments	2,135	2,577
Long-term investments	0	794
Cash
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	35,451	57,137
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	35,451	57,137
Cash and Cash Equivalents	35,451	57,137
Short-term investments	0	0
Long-term investments	0	0
Money Market Funds | Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	260	2,389
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	260	2,389
Cash and Cash Equivalents	260	2,389
Short-term investments	0	0
Long-term investments	0	0
Corporate Bonds | Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	34,564	36,406
Gross Unrealized Gains	7	0
Gross Unrealized Losses	(15)	(70)
Fair Value	34,556	36,336
Cash and Cash Equivalents	765	0
Short-term investments	29,975	35,677
Long-term investments	$ 3,824	$ 729