How long do job offer letters take?

So I got a verbal job offer, which I accepted, and then the recruiter said that they will officially mail me the offer in writing. It's been one week, and I haven't gotten anything. It's a large corporation with tens of thousands of people. My job site is located in Bellevue, WA, but they need approval from their headquarters in East Asia for all hires.

Is this typical at all? This will be the first time I'm an employee for a company with more than 10 people, lol.