Accumulated other comprehensive loss 2 of 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized investment gain (loss) at beginning of year	$ 883
Other comprehensive income (loss) before reclassification	(6,485)
Amounts reclassified from other comprehensive loss to net income	(16,421)
Net unrealized investment gain at end of year	0	$ 883
Unrealized Investment Gain
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized investment gain (loss) at beginning of year	888	699	$ 631
Other comprehensive income (loss) before reclassification	0	189	173
Amounts reclassified from other comprehensive loss to net income	0	0	(105)
Net change in unrealized gain (loss) on investments	(888)	189	68
Net unrealized investment gain at end of year	0	888	699
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from other comprehensive loss to net income	0
Net unrealized investment gain at end of year	$ 888
Accounting Standards Update 2016-01 [Member] | Unrealized Investment Gain
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from other comprehensive loss to net income		$ 0	$ 0