Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized cost of investment securities available-for-sale	$ 657,631	$ 640,455
Fair value of investment securities held-to-maturity	$ 467,372	$ 475,134
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Treasury stock, shares	12,345,000	12,196,000
Common Class A
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	37,207,000	37,012,000
Common stock, shares outstanding	26,635,000	26,589,000
Common Class B
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	18,327,000	18,327,000
Common stock, shares outstanding	16,554,000	16,554,000