Cash, Cash Equivalents, and Investments - Summary of Cash, Cash Equivalents and Held-to-Maturity Investments by Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	$ 114,063	$ 118,305
Gross Unrealized Gains	18	11
Gross Unrealized Losses	(30)	(79)
Fair Value	114,051	118,237
Cash and Cash Equivalents	53,365	59,526
Short-term investments	50,689	50,254
Long-term investments	10,009	8,525
State and Municipal Obligations
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	20,465	19,002
Gross Unrealized Gains	11	11
Gross Unrealized Losses	(2)	(9)
Fair Value	20,474	19,004
Cash and Cash Equivalents	0	0
Short-term investments	18,060	12,000
Long-term investments	2,405	7,002
Certificates of Deposit
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	3,355	3,371
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	3,355	3,371
Cash and Cash Equivalents	0	0
Short-term investments	3,010	2,577
Long-term investments	345	794
Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	38,758	38,795
Gross Unrealized Gains	7	0
Gross Unrealized Losses	(28)	(70)
Fair Value	38,737	38,725
Cash and Cash Equivalents	1,880	2,389
Short-term investments	29,619	35,677
Long-term investments	7,259	729
Fair Value, Inputs, Level 2
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	23,820	22,373
Gross Unrealized Gains	11	11
Gross Unrealized Losses	(2)	(9)
Fair Value	23,829	22,375
Cash and Cash Equivalents	0	0
Short-term investments	21,070	14,577
Long-term investments	2,750	7,796
Cash
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	51,485	57,137
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	51,485	57,137
Cash and Cash Equivalents	51,485	57,137
Short-term investments	0	0
Long-term investments	0	0
Money Market Funds
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost		2,389
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		2,389
Cash and Cash Equivalents		2,389
Short-term investments		0
Long-term investments		0
Money Market Funds | Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	1,880
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	1,880
Cash and Cash Equivalents	1,880
Short-term investments	0
Long-term investments	0
Corporate Bonds
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost		36,406
Gross Unrealized Gains		0
Gross Unrealized Losses		(70)
Fair Value		36,336
Cash and Cash Equivalents		0
Short-term investments		35,677
Long-term investments		$ 729
Corporate Bonds | Fair Value, Inputs, Level 1
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	36,878
Gross Unrealized Gains	7
Gross Unrealized Losses	(28)
Fair Value	36,857
Cash and Cash Equivalents	0
Short-term investments	29,619
Long-term investments	$ 7,259