Here is the main cold wallet of Bitstamp: https://blockchain.info/address/1JoktQJhCzuCQkt3GnQ8Xddcq4mUgNyXEa

From the earliest transaction of the address: https://blockchain.info/tx/8f1d3a8ef6b2d4a25d2f499279e01518b4770819ccbc39a765c4c326170c61b3

the source addresses and destination address are all cold wallets of Bitstamp.  The total amount of these cold wallets are about 200K.

The 18k BTC lost is about 10% of total reserve of Bitstamp.