Fair Value Measurements - Contractual Maturities of Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Maturing in one year or less	$ 957	$ 1,645
Maturing in second year through fifth year	23,162	24,649
Maturing in sixth year through tenth year	17,008	14,769
Maturing after ten years	37,381	35,299
Total debt securities	$ 78,508	$ 76,362

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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