Securities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale of Available-for-sale Securities, Debt	$ 40,421,000	$ 60,314,000	$ 21,527,000
Available-for-sale Securities, Gross Realized Gains	454,000	633,000	456,000
Available-for-sale Securities, Gross Realized Losses	$ 86,000	472,000
Collateral Underlying Mortgage Investments Terms	30- and 15-year fixed and 10/1 adjustable rate mortgage
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	$ 35,900,000
Cost Method Investments, Fair Value Disclosure	35,900,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	862,873,000	698,059,000
Accumulated unrealized losses	18,443,000	12,703,000
Securities Available For Sale Transferred To Held-To-Maturity	92,100,000		158,800,000
Available For Sale Securities Transferred To Held To Maturity Securities Unrealized Gain Loss	0	0	$ (3,137,000)
Trading Securities, Unrealized Holding Loss	1,800,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	664,476,000	443,830,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 13,451,000	$ 6,030,000
Common Stock, Shares, Outstanding	38,021,835	34,351,409
Debt Instrument, Convertible, Conversion Price	$ 1.6483
Common Class B [Member]
Schedule of Available-for-sale Securities [Line Items]
Common Stock, Shares, Outstanding	11,330
Common Class A [Member]
Schedule of Available-for-sale Securities [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities	18,675
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,800,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	22,800,000	$ 38,900,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	400,000	$ 400,000
Carrying Amount [Member] | Repurchase Agreement [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	204,200,000
Carrying Amount [Member] | United States Treasury Deposits and Other Public and Trust Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	193,800,000
Mortgage Backed Securities And Collateralized Mortgage Obligations Of Us Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	634,200,000
Accumulated unrealized losses	13,900,000
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	59,900,000
Accumulated unrealized losses	1,000,000
Private Collateralized Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	76,700,000
Accumulated unrealized losses	$ 1,700,000