Credit Agreement (Details)	Feb. 26, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)
Credit Agreement
Amount outstanding		$ 140,000,000	$ 140,000,000
Line of Credit | Credit Agreement
Credit Agreement
Principal amount	$ 250,000,000.0
Amount outstanding		$ 140,000,000
Margin rate (as a percent)	0.50%
Effective interest rate (as a percent)		2.03%
Maximum leverage ratio	3.0
Minimum interest coverage ratio	3.0
Line of Credit | Credit Agreement | Minimum
Credit Agreement
Commitment fee percentage (as a percent)	0.20%
Line of Credit | Credit Agreement | Maximum
Credit Agreement
Commitment fee percentage (as a percent)	0.30%
Line of Credit | Credit Agreement | Federal Funds Effective Rate
Credit Agreement
Variable rate spread (as a percent)	0.50%
Line of Credit | Credit Agreement | Adjusted LIBOR
Credit Agreement
Variable rate spread (as a percent)	1.00%
Margin rate (as a percent)	1.50%