Common Stock Repurchase Plans (Details) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended		6 Months Ended
	Apr. 30, 2015	Nov. 30, 2014	Jun. 30, 2015	Apr. 30, 2015	Jun. 30, 2014
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount	$ 50,000,000.0	$ 100,000,000		$ 50,000,000.0
Payments for repurchase of common stock		$ 100,000,000	$ 19,013,000		$ 49,804,000
Acquisition of treasury stock (in shares)	1.8	6.5	1.5	8.3
Share repurchase plan, percent of common shares outstanding, expected to be delivered		80.00%
Treasury stock aquired, average cost per share	$ 12.05		$ 12.36
Stock repurchase program, Number of shares authorized to be repurchased, percent of shares outstanding	2.30%