Stockholders' Equity - Common stock repurchased (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity [Abstract]
Shares repurchased related to employee stock-based compensation plans (in shares)	371,165	136,173	1,763,092	2,900,266
Average purchase price per share (in dollars per share)	$ 7.22	$ 8.88	$ 6.35	$ 9.76
Common shares issued (in shares)	561,100	361,779	3,727,574	5,569,853