Stock-Based Compensation (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted non-statutory stock options to key employees			60,500
Non-statutory stock options, weighted average exercise price			$ 36.74
Vesting period, years			3 years
Contractual terms, years			10 years
Stock-based compensation expense	$ 788	$ 887	$ 2,518	$ 2,648
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	0		36,400
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
Common stock issuable per RSU granted			1
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years			3 years
Non-Employee Directors Service-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years			2 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	$ 26		$ 67