Fair Value Measurements and Derivative Instruments (Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 218,512	$ 270,313
Gross unrealized gains	4,327	218
Gross unrealized losses	(719)	(5,202)
Estimated fair value	222,120	265,329
Government and related securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	80,732	109,776
Gross unrealized gains	1,358	47
Gross unrealized losses	(114)	(1,336)
Estimated fair value	81,976	108,487
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	70,426	58,714
Gross unrealized gains	2,009	4
Gross unrealized losses	(286)	(1,780)
Estimated fair value	72,149	56,938
Commingled fixed income securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,675	1,637
Gross unrealized gains	0	0
Gross unrealized losses	(19)	(67)
Estimated fair value	1,656	1,570
Mortgage-backed / asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	65,679	100,186
Gross unrealized gains	960	167
Gross unrealized losses	(300)	(2,019)
Estimated fair value	$ 66,339	$ 98,334

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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