Fair value of financial instruments (Details) - USD ($) $ in Thousands	6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 79,400		$ 81,039
Accretion of net premium on short-term investments	113	$ 237
Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	76,773		77,598
Short-term investments: | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,733		4,239
Short-term investments: | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,975		1,473
Short-term investments: | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,026		2,537
Short-term investments: | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	9,435		9,705
Short-term investments: | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	5,520		7,982
Short-term investments: | Foreign government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value			750
Short-term investments: | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	52,084		50,912
Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,627		3,441
Cash equivalents | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	631		444
Cash equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,996		2,997
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,606		1,917
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,975		1,473
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,975		1,473
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | Foreign government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value			0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments: | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	631		444
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	631		444
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	75,794		79,122
Significant Other Observable Inputs (Level 2) | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	73,798		76,125
Significant Other Observable Inputs (Level 2) | Short-term investments: | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,733		4,239
Significant Other Observable Inputs (Level 2) | Short-term investments: | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Other Observable Inputs (Level 2) | Short-term investments: | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,026		2,537
Significant Other Observable Inputs (Level 2) | Short-term investments: | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	9,435		9,705
Significant Other Observable Inputs (Level 2) | Short-term investments: | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	5,520		7,982
Significant Other Observable Inputs (Level 2) | Short-term investments: | Foreign government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value			750
Significant Other Observable Inputs (Level 2) | Short-term investments: | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	52,084		50,912
Significant Other Observable Inputs (Level 2) | Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,996		2,997
Significant Other Observable Inputs (Level 2) | Cash equivalents | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Other Observable Inputs (Level 2) | Cash equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,996		2,997
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Short-term investments: | Foreign government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value			0
Significant Unobservable Inputs (Level 3) | Short-term investments: | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Cash equivalents | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0		0
Significant Unobservable Inputs (Level 3) | Cash equivalents | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 0		$ 0