INVESTMENTS - Summary of Investment Securities by Estimated Maturity (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Held-to-Maturity Amortized Cost
Due in one year or less	$ 215
Due after one year through five years	409,559
Due after five years through ten years	258,526
Due after ten years	793
Total	669,093	770,755
Held-to-Maturity Market Value
Due in one year or less	218
Due after one year through five years	407,787
Due after five years through ten years	252,762
Due after ten years	918
Held-to-Maturity Market Value	661,685	778,474
Available-for-Sale Amortized Cost
Due in one year or less	5,009
Due after one year through five years	250,089
Due after five years through ten years	361,949
Due after ten years	258,881
Total	875,928	1,017,104
Available-for-Sale Market Value
Due in one year or less	5,152
Due after one year through five years	251,177
Due after five years through ten years	351,776
Due after ten years	246,642
Available-for-Sale Market Value	$ 854,747	$ 1,032,096