Schedule of Short-Term Borrowings Activity (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Short Term Debt [Line Items]
Average borrowings	$ 432,064	$ 277,952
Maximum borrowings outstanding	$ 1,129,250	$ 534,700
Weighted average interest rates, computed on a daily basis	0.37%	0.49%
Weighted average interest rates, ending balance	0.36%	0.46%