Cash, Cash Equivalents, and Investments - Summary of Cash, Cash Equivalents and Held-to-Maturity Investments by Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	$ 102,480	$ 118,305
Gross Unrealized Gains	4	11
Gross Unrealized Losses	(43)	(79)
Fair Value	102,441	118,237
Cash and Cash Equivalents	50,600	59,526
Short-term investments	45,620	50,254
Long-term investments	6,260	8,525
Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	40,494	38,795
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(35)	(70)
Fair Value	40,462	38,725
Cash and Cash Equivalents	4,808	2,389
Short-term investments	29,911	35,677
Long-term investments	5,775	729
Fair Value, Inputs, Level 2
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	16,194	22,373
Gross Unrealized Gains	1	11
Gross Unrealized Losses	(8)	(9)
Fair Value	16,187	22,375
Cash and Cash Equivalents	0	0
Short-term investments	15,709	14,577
Long-term investments	485	7,796
Fair Value, Inputs, Level 2 | State and Municipal Obligations
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	15,152	19,002
Gross Unrealized Gains	1	11
Gross Unrealized Losses	(8)	(9)
Fair Value	15,145	19,004
Cash and Cash Equivalents	0	0
Short-term investments	14,667	12,000
Long-term investments	485	7,002
Fair Value, Inputs, Level 2 | Certificates of Deposit
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	1,042	3,371
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,042	3,371
Cash and Cash Equivalents	0	0
Short-term investments	1,042	2,577
Long-term investments		794
Cash
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	45,792	57,137
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	45,792	57,137
Cash and Cash Equivalents	45,792	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	4,163	2,389
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	4,163	2,389
Cash and Cash Equivalents	4,163	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	36,331	36,406
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(35)	(70)
Fair Value	36,299	36,336
Cash and Cash Equivalents	645	0
Short-term investments	29,911	35,677
Long-term investments	$ 5,775	$ 729