Commitments and Contingent Liabilities - Narrative (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) Jurisdiction	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Commitments And Contingent Liabilities [Line Items]
Total minimum rent expense	$ 7,200,000	$ 7,700,000	$ 8,300,000
Contingent rent expense	$ 0	0	$ 0
Future operating lease, term	15 years
Material capital leases	$ 0	$ 0
Letter of credit, outstanding	$ 455,700,000
Number of jurisdiction | Jurisdiction	30
Letter of Credit [Member]
Commitments And Contingent Liabilities [Line Items]
Letter of credit, outstanding	$ 507,000,000
Line of credit facility, agreement term	14 years
Minimum [Member]
Commitments And Contingent Liabilities [Line Items]
Future operating lease, amount	$ 4,500,000
Maximum [Member]
Commitments And Contingent Liabilities [Line Items]
Future operating lease, term	15 years
Future operating lease, amount	$ 5,600,000
Letter Of Credit Initial Amount [Member] | Letter of Credit [Member]
Commitments And Contingent Liabilities [Line Items]
Letter of credit, outstanding	$ 450,000,000