Stockholders' Equity - Treasury Stock (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Shares purchased during period (shares)	131,012
Average price paid per share (usd per share)	$ 13.77
Commissions paid to acquire shares	$ 5,240
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares purchased during period (shares)	131,012
Treasury stock acquired during period	$ 4,749,000	$ 6,555,000