TOPIC 606 ADOPTION IMPACT AND REVENUE FROM CONTRACTS WITH CUSTOMERS: Narrative (Details) - USD ($)	3 Months Ended
	Jun. 30, 2018	Apr. 01, 2018	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 638,043,000		$ 628,331,000
Capitalized contract cost, unamortized	18,100,000
Capitalized contract cost, net	2,900,000
Contract with customer, asset, credit loss expense	0
ASC 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ (14,611,000)	$ 12,700,000
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost amortization period	2 years
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost amortization period	5 years