Common Stock - Stock Repurchase Program (Details) - USD ($)	3 Months Ended		34 Months Ended	65 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 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
Credit Facility
Equity, Class of Treasury Stock [Line Items]
Share repurchase covenant	$ 9,700,000
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			$ 300,000