Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost	$ 3,472,642	$ 3,451,149
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	45,560,960	45,365,170
Common stock, shares outstanding	45,520,541	45,336,278
Treasury stock, shares	40,419	28,892
Variable Interest Entity, Primary Beneficiary [Member]
Long-term debt	$ 5,401,992	$ 5,268,596
Equity investments in pooled funds [Member]
Other Investment Not Readily Marketable, Fair Value	$ 387,045	$ 351,049

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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