Debt (Narratives) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Line of Credit Facility [Line Items]
New Credit Agreement 2017	$ 545,000,000		$ 545,000,000
Income tax expense as a percentage of income from continuing operations	213.00%	67.00%	65.00%	36.00%
Maximum availability under New Revolving Credit Facility	$ 100,000,000		$ 100,000,000
Outstanding borrowings	390,463,000		390,463,000
Debt Instrument, Periodic Payment, Principal	1,113,000		3,338,000
Current portion of long term debt	60,134,000		60,134,000			$ 52,568,000
Deferred Costs	14,690,000		14,690,000
Capital Lease Obligations	193,000		193,000			551,000
Accumulated Amortization, Deferred Finance Costs	1,924,000		1,924,000			350,000
Unsecured credit lines	5,038,000		5,038,000
Amount drawn on unsecured credit lines			0
Long-term Debt and Capital Lease Obligations, Current	134,000		134,000
Proceeds from Secured Lines of Credit			445,000,000
Replaced Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Deferred Costs	645,000		645,000
Voluntary Debt Payment [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Periodic Payment, Principal	13,700,000		38,700,000
Current portion of long term debt	60,000,000		60,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Deferred Costs	2,789,000		2,789,000
Accumulated Amortization, Deferred Finance Costs	511,000		511,000			$ 93,000
New Revolving Credit Facility
Line of Credit Facility [Line Items]
Outstanding letters of credit	5,590,000		5,590,000
Current portion of long term debt	4,450,000		4,450,000
New Revolving Credit Facility | Standby Letters of Credit
Line of Credit Facility [Line Items]
Outstanding letters of credit	4,566,000		4,566,000
New Revolving Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Outstanding letters of credit	1,024,000		1,024,000
New Revolving Credit Facility | Unsecured Lines of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	16,751,000		16,751,000
Outstanding borrowings	$ 10,238,000		$ 10,238,000
Scenario, Forecast [Member]
Line of Credit Facility [Line Items]
Income tax expense as a percentage of income from continuing operations					32.00%