Stock Option and Compensation Plans - Summary of Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock Options
Outstanding at beginning of year (in shares)	5,284	3,359	3,009
Granted (in shares)	1,293	3,024	972
Exercised (in shares)	0	(20)	(428)
Expired or forfeited (in shares)	(674)	(1,079)	(194)
Outstanding at end of year (in shares)	5,903	5,284	3,359
Weighted Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 19.58	$ 39.92	$ 30.43
Granted (in dollars per share)	1.67	3.50	60.40
Exercised (in dollars per share)	0.00	1.64	15.73
Expired or forfeited (in dollars per share)	36.54	38.17	48.63
Outstanding at end of year (in dollars per share)	$ 13.72	$ 19.58	$ 39.92
Options exercisable at end of year (in shares)	2,709	1,954	1,531
Weighted average grant date fair value (per share) of options granted during the period (in dollars per share)	$ 1.20	$ 2.45	$ 38.18