A 64-year-old man has severe polyuria and polydipsia, drinking 3 to 4 glasses of water and producing over 0.5 liters of urine each hour. Rajesh a new medicine resident places the patient on overnight water restriction for fuher analysis. The test results shown below were obtained the following morning. Plasma sodium concentration: 155 mEq/L Urine osmolarity: 90 mOsmol/L Urine glucose concentration: 0 mg/dL Which of the following is the most likely diagnosis?