INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of income tax expense reported to amount computed by applying the U.S. federal tax rate
Provision for income taxes at the statutory rate of 35%	$ (302)	$ 10,900	$ 20,866	$ 41,677
Excess tax benefit on share-based compensation	(477)		(3,711)
Tax-exempt interest income	(1,187)	(1,020)	(3,525)	(3,149)
Dividends received deduction	(553)	(626)	(1,488)	(1,676)
ESOP dividends paid deduction	(240)	(238)	(724)	(714)
Other items, net	163	(137)	429	205
Total tax expense (benefit)	$ (2,596)	$ 8,879	$ 11,847	$ 36,343
Reconciliation of income tax expense rate to the U.S. federal tax rate
U.S. federal tax rate (as a percent)	35.00%	35.00%	35.00%	35.00%
Excess tax benefit on share-based compensation	55.30%	0.00%	(6.20%)	0.00%
Effective rate reduction due to tax exempt interest income (as a percent)	137.70%	(3.20%)	(5.90%)	(2.60%)
Effective rate reduction due to dividend received (as a percent)	64.20%	(2.00%)	(2.50%)	(1.40%)
Effective rate reduction due to dividend paid to ESOP (as a percent)	27.90%	(0.80%)	(1.20%)	(0.60%)
Effective rate reduction due to other items, net (as a percent)	(18.90%)	(0.50%)	0.70%	0.10%
Effective Income Tax Rate Reconciliation, Percent, Total	301.20%	28.50%	19.90%	30.50%