What does the balance mean in EtherScan?

2018-07-21 19:05:26

For example, IDEX has 40,767.582633880607462483 Ether. But I use BalanceAt function and only get 15.884 Ether. Why? Should I traversal all the tokens and query balanceOf("0x2a0c0DBEcC7E4D658f48E01e3fA353F44050c208")?