Shareholders' Equity - Additional Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee Stock Purchase Plan (ESPP): Maximum annual contribution per employee	10.00%
Employee Stock Purchase Plan (ESPP), Shares in ESPP	136,000
Employee Stock Purchase Plan (ESPP), Shares purchased	44,000	37,000	24,000
Employee Stock Purchase Plan (ESPP), Weighted average purchase price	$ 4.91	$ 7.38	$ 13.35
Remaining shares from the trusts recorded as treasury stock	11,077,779	8,014,004
Stock trusts, shares	0	3,264,651
Preferred stock, shares authorized	2,500,000	2,500,000
Preferred stock, par or stated value per share	$ 0.01	$ 0.01
Preferred stock, shares outstanding	0	0
Stock Employee Compensation Trust (SECT) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares from the trusts recorded as treasury stock	2,700,000
Shares released from employee stock trust	503,000	98,000	0
Shares purchased by employee stock trust	0	0	0
Stock trusts, shares		3,200,000	3,300,000
Omnibus Stock Trust (OST) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares from the trusts recorded as treasury stock	59,000
Shares released from employee stock trust	0	0	0
Shares purchased by employee stock trust	0	0	0
Stock trusts, shares		59,000	59,000