A Dash-8 Captain reported detecting smoke in the cockpit; so an emergency was declared and the flight diverted to a nearby airport.

Narrative

In cruise at FL190; the First Officer and I detected a smoke-like odor followed by visual confirmation of smoke in the flight deck. We performed the oxygen mask donning procedure; declared an emergency with Center; and requested diversion to [a nearby airport]. We performed the 'smoke in aircraft' emergency procedure checklist and informed the Flight Attendant that we were diverting for smoke in the cockpit.The Flight Attendant told the First Officer that there was no smoke in the cabin; we could hear the lavatory smoke alarm sounding intermittently. As we were descending and diverting; the smoke and the odor gradually dissipated; probably because we had turned off the environmental system. I had the First Officer inform the Flight Attendant to prepare the cabin for a normal landing and advise us when the cabin was prepared for landing. I also informed the Approach Controller that we no longer had any smoke in the cockpit.The Flight Attendant then advised that there was a little smoke in the cabin. On approach; the Flight Attendant called us back to inform us the cabin was secured. After a normal ILS approach and landing; we cleared the runway and came to a complete stop. Checked that there were no smoke indications; visual and/or odor; in both the flight deck and with the Flight Attendant in the cabin. I then taxied the airplane to the terminal and we proceeded with a normal passenger deplaning once at the gate.