Short-Term Borrowings and Long-Term Debt - Outstanding Short Term Borrowings and Long Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Debt Outstanding [Line Items]
Short-term borrowings	$ 6,630		$ 5,080
Total long-term debt	453,764		455,216
Other short-term borrowings
Debt Outstanding [Line Items]
Principal value	6,630	[1]
Short-term borrowings	6,630	[1]	5,080	[1]
5.375% Senior Notes
Debt Outstanding [Line Items]
Maturity	Sep. 15, 2020
Principal value	350,000
Senior Notes	348,378		348,209
6.05% Subordinated Notes
Debt Outstanding [Line Items]
Maturity	Jun. 01, 2017	[2]
Principal value	45,964	[2]
Subordinated Notes	50,497	[2]	51,987	[2]
7.0% Junior Subordinated Debentures
Debt Outstanding [Line Items]
Maturity	Oct. 15, 2033
Principal value	50,000
Junior Subordinated Debentures	$ 54,889		$ 55,020

[1] Represents cash collateral received from certain counterparties in relation to market value exposures of derivative contracts in our favor, primarily for our interest rate swap agreement related to our 6.05% Subordinated Notes.

[2] At September 30, 2014 and December 31, 2013, included in the carrying value of our 6.05% Subordinated Notes was an interest rate swap valued at $5.0 million and $6.5 million, respectively, related to hedge accounting associated with the notes.