What is the ruling on one who propagates ideas of disbelief?

Anyone who propagates kufr ideas, such as attacking the religion, or claiming that Sharia is not fit to govern, or advocating for the separation of religion and state, or mocking the Prophet, peace and blessings be upon him, and spreads them among people, disbelieves by this action, even if he was joking. Allah, the Almighty, says: "And if you ask them, they will surely say, 'We were only conversing and jesting.' Say, 'Is it in Allah and His verses and His Messenger that you were mocking?' Make no excuse; you have disbelieved after your belief." If it is established that what this person advocates is disbelief, then the ruler must be informed about him so that the rulings of an apostate may be applied to him.