Stock-Based Compensation (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years			3 years
Granted non-statutory stock options to key employees			60,500
Non-statutory stock options, weighted average exercise price			$ 36.74
Contractual terms, years			10 years
Stock-based compensation expense	$ 869	$ 776	$ 1,730	$ 1,761
Non-Employee Directors Service-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service-based restricted stock units to non-employee directors	11,200
Vesting period, years	2 years
Common stock issuable per RSU granted	1
Employee Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awarded in period			75,600
Employee And Non Employee Director Service Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awarded in period			25,200
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years			3 years
Employee Performance Based Restricted Stock Tracking Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units non vested grants			9,486
Employee Service Based Restricted Stock Tracking Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units non vested grants			3,264
Restricted Stock Tracking Units RSTU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years			3 years
Stock-based compensation expense	$ 24		$ 41