Common Stock - Stock Repurchase Program (Details) - USD ($)	3 Months Ended		6 Months Ended		37 Months Ended	68 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2015	Nov. 30, 2012
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, remaining amount	$ 49,700,000		$ 49,700,000		$ 49,700,000	$ 49,700,000
Share Repurchase Program, November 2012
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount (up to)								$ 25,000,000
Repurchase of common stock						$ 25,000,000
Repurchase of common stock during period (in shares)	0		0
Share Repurchase Program, June 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount (up to)							$ 50,000,000
Repurchase of common stock		$ 500,000		$ 500,000	$ 300,000
Average cost per share (in dollars per share)		$ 9.76		$ 9.76
Repurchase of common stock during period (in shares)		50,000		50,000