Employee Benefit Plans - Changes in projected benefit obligation, plan assets and funded status (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014
Change in projected benefit obligation
Projected benefit obligation at beginning of year	$ 62,605	$ 57,599
Service cost	2,939	2,954	$ 2,457
Interest cost	2,893	2,618	2,333
Benefits paid	(1,271)	(1,116)
Actuarial (gain) loss	8,498	550
Projected benefit obligation at end of year	75,664	62,605	57,599
Change in plan assets
Fair value of plan assets at beginning of year	44,032	39,581
Actual return on plan assets	(1,202)	(1,248)
Employer contributions	12,734	6,815
Benefits paid	(1,271)	(1,116)
Fair value of plan assets at end of year	54,293	44,032	$ 39,581
Funded status at end of year	$ (21,371)	$ (18,573)