Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Securities available-for-sale [Abstract]
Amortized Cost	$ 2,436,751,000	$ 1,310,071,000
Gross Unrealized Gains	10,966,000	8,557,000
Gross Unrealized Losses	20,683,000	20,082,000
Securities available-for-sale, at fair value	2,427,034,287	1,298,546,056
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	31,917,000
Due in one year to five years	82,347,000
Due in five years to ten years	166,329,000
Due after ten years	416,840,000
Mortgage-backed securities	1,548,758,000
Asset-backed securities	190,560,000
Amortized Cost	2,436,751,000
Available-for-sale, Fair Value [Abstract]
Due in one year or less	31,811,000
Due in one year to five years	83,312,000
Due in five years to ten years	168,799,000
Due after ten years	413,842,000
Mortgage-backed securities	1,539,050,000
Asset-backed securities	190,220,000
Securities available-for-sale, at fair value	2,427,034,287	1,298,546,056
Securities held-to-maturity [Abstract]
Amortized Cost	21,163,360	25,251,316
Gross Unrealized Gains	199,000	87,000
Gross Unrealized Losses	40,000	105,000
Securities held-to-maturity, fair value	21,322,047	25,233,254
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	1,021,000
Due in one year to five years	6,603,000
Due in five years to ten years	10,219,000
Due after ten years	3,320,000
Mortgage-backed securities	0
Asset-backed securities	0
Amortized Cost	21,163,360	25,251,316
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	1,023,000
Due in one year to five years	6,631,000
Due in five years to ten years	10,323,000
Due after ten years	3,345,000
Mortgage-backed securities	0
Asset-backed securities	0
Fair Value	21,322,047	25,233,254
U.S. Treasury securities
Securities available-for-sale [Abstract]
Amortized Cost	250,000	250,000
Gross Unrealized Gains	1,000	0
Gross Unrealized Losses	0	0
Securities available-for-sale, at fair value	251,000	250,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	251,000	250,000
U.S. government agency securities
Securities available-for-sale [Abstract]
Amortized Cost	62,659,000	22,306,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	759,000	537,000
Securities available-for-sale, at fair value	61,900,000	21,769,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	61,900,000	21,769,000
Mortgage-backed securities
Securities available-for-sale [Abstract]
Amortized Cost	1,548,758,000	988,008,000
Gross Unrealized Gains	5,440,000	4,304,000
Gross Unrealized Losses	15,148,000	15,686,000
Securities available-for-sale, at fair value	1,539,050,000	976,626,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	1,539,050,000	976,626,000
State and municipal securities
Securities available-for-sale [Abstract]
Amortized Cost	532,508,000	211,581,000
Gross Unrealized Gains	5,209,000	4,103,000
Gross Unrealized Losses	4,115,000	2,964,000
Securities available-for-sale, at fair value	533,602,000	212,720,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	533,602,000	212,720,000
Asset-backed securities
Securities available-for-sale [Abstract]
Amortized Cost	190,560,000	79,318,000
Gross Unrealized Gains	134,000	111,000
Gross Unrealized Losses	474,000	849,000
Securities available-for-sale, at fair value	190,220,000	78,580,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	190,220,000	78,580,000
Corporate notes and other
Securities available-for-sale [Abstract]
Amortized Cost	102,016,000	8,608,000
Gross Unrealized Gains	182,000	39,000
Gross Unrealized Losses	187,000	46,000
Securities available-for-sale, at fair value	102,011,000	8,601,000
Available-for-sale, Fair Value [Abstract]
Securities available-for-sale, at fair value	102,011,000	8,601,000
State and municipal securities
Securities held-to-maturity [Abstract]
Amortized Cost	21,163,000	25,251,000
Gross Unrealized Gains	199,000	87,000
Gross Unrealized Losses	40,000	105,000
Securities held-to-maturity, fair value	21,322,000	25,233,000
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	21,163,000	25,251,000
Held-to-maturity, Fair Value [Abstract]
Fair Value	$ 21,322,000	$ 25,233,000