INVESTMENTS - Summary of Investment Securities by Estimated Maturity (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Held-to-Maturity Amortized Cost
Due in one year or less	$ 156
Due after one year through five years	365,819
Due after five years through ten years	399,321
Due after ten years	125,510
Total	890,806	837,272
Held-to-Maturity Market Value
Due in one year or less	158
Due after one year through five years	364,424
Due after five years through ten years	394,238
Due after ten years	126,507
Held-to-Maturity Market Value	885,327	824,985
Available-for-Sale Amortized Cost
Due in one year or less	7,060
Due after one year through five years	290,533
Due after five years through ten years	256,653
Due after ten years	333,446
Total	887,692	945,052
Available-for-Sale Market Value
Due in one year or less	7,359
Due after one year through five years	289,018
Due after five years through ten years	247,950
Due after ten years	318,199
Available-for-Sale Market Value	$ 862,526	$ 913,601