ACCOUNTING STANDARDS RECENTLY ISSUED OR ADOPTED Available for sale securities - equity securities (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Securities—available-for-sale	$ 1,412,273,000	$ 919,485,000
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities—available-for-sale		5,578,000
Reported Value Measurement [Member]
Debt Securities, Available-for-sale [Line Items]
Equity Securities, FV-NI	416,000	0
Securities—available-for-sale	$ 1,412,273,000	$ 919,485,000