Fair Value Measurements and Derivative Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 309,058	$ 325,368
Gross unrealized gains	6,120	3,504
Gross unrealized losses	(2,322)	(6,580)
Estimated fair value	312,856	322,292
Amortized cost - Within 1 year	23,296
Estimated fair value - Within 1 year	23,356
Amortized cost - After 1 year through 5 years	47,382
Estimated fair value - After 1 year through 5 years	48,261
Amortized cost - After 5 years through 10 years	85,913
Estimated fair value - After 5 years through 10 years	87,204
Amortized cost - After 10 years	152,467
Estimated fair value - After 10 years	154,035
Amortized cost - Total	309,058
Estimated fair value - Total	312,856
Debt securities - U.S. and foreign governments, agencies and municipalities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	102,854	121,803
Gross unrealized gains	1,986	999
Gross unrealized losses	(878)	(3,372)
Estimated fair value	103,962	119,430
Debt securities - corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	58,914	37,901
Gross unrealized gains	1,771	935
Gross unrealized losses	(130)	(572)
Estimated fair value	60,555	38,264
Mortgage-backed / asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	147,290	165,664
Gross unrealized gains	2,363	1,570
Gross unrealized losses	(1,314)	(2,636)
Estimated fair value	$ 148,339	$ 164,598