Stockholders' Equity - Reconciliation of Common Stock (Details) - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period (in shares)	18,634,502	18,085,798
Issuance of common stock (in shares)	143,600	334,700
Restricted stock-based awards (in shares)	84,690	214,004
Balance, end of period (in shares)	18,862,792	18,634,502