Significant Accounting Policies (Cash and Cash Equivalents, Investments and Fair Value of Financial Instruments) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accounting Policies [Abstract]
Checks outstanding	$ 0		$ 0		$ 0
Losses recognized from other-than-temporary impairments	0	$ 0	0	$ 0
Fair value of fixed rate borrowings	418,500,000		418,500,000		437,000,000
Fair value of variable rate borrowings	$ 210,000,000		$ 210,000,000		$ 100,000,000