Stockholders' Equity - Common stock repurchased (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Equity [Abstract]
Shares repurchased related to employee stock-based compensation plans (in shares)	263,218	1,374,997	1,391,927	2,764,093
Average purchase price per share (in dollars per share)	$ 6.68	$ 10.14	$ 6.12	$ 9.80
Common shares issued (in shares)	425,495	2,077,235	3,166,474	5,208,074