Stockholders' Equity Stock Repurchases (Details) - USD ($)	3 Months Ended		60 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	May 23, 2016	Apr. 10, 2013
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period (in shares)			1,640,012
Stock repurchased during period, value			$ 27,700,000
Remaining authorized repurchase amount	$ 12,300,000		$ 12,300,000
April 2013 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Authorized amount					$ 20,000,000.0
May 2016 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Authorized amount				$ 20,000,000.0
Share Repurchase Programs
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and retired during period (in shares)	0	297,223
Stock repurchased during period, value		$ 5,100,000
Average cost per share (in dollars per share)		$ 17.08