Investments Schedule of Available-for-sale and Held-to-Maturity Securities (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		$ 1,165,906	$ 1,084,105
Available-for-sale Securities, Gross Unrealized Gains		26,808	7,634
Available-for-sale Securities, Gross Unrealized Losses		(1,191)	(7,229)
Available-for-sale securities at fair value		1,191,523	1,084,510
Held-to-maturity Securities		105,297	116,352
Held-to-maturity Securities, Unrecognized Holding Gain		2,092	294
Held-to-maturity Securities, Unrecognized Holding Loss		0	(262)
Held-to-maturity Securities, Fair Value		107,389	116,384
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		40,822	21,214
Available-for-sale Securities, Gross Unrealized Gains		920	64
Available-for-sale Securities, Gross Unrealized Losses		(5)	(27)
Available-for-sale securities at fair value		41,737	21,251
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		335,632	345,033
Available-for-sale Securities, Gross Unrealized Gains		7,578	874
Available-for-sale Securities, Gross Unrealized Losses		0	(1,345)
Available-for-sale securities at fair value		343,210	344,562
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		265,507	263,661
Available-for-sale Securities, Gross Unrealized Gains		10,877	5,099
Available-for-sale Securities, Gross Unrealized Losses		(68)	(116)
Available-for-sale securities at fair value		276,316	268,644
Mortgage Backed Securities, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	[1]	503,993	431,446
Available-for-sale Securities, Gross Unrealized Gains	[1]	7,145	1,329
Available-for-sale Securities, Gross Unrealized Losses	[1]	(1,109)	(5,734)
Available-for-sale securities at fair value	[1]	510,029	427,041
Held-to-maturity Securities	[1]	105,297	116,352
Held-to-maturity Securities, Unrecognized Holding Gain	[1]	2,092	294
Held-to-maturity Securities, Unrecognized Holding Loss	[1]	0	(262)
Held-to-maturity Securities, Fair Value	[1]	107,389	116,384
Other Aggregated Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		19,952	22,751
Available-for-sale Securities, Gross Unrealized Gains		288	268
Available-for-sale Securities, Gross Unrealized Losses		(9)	(7)
Available-for-sale securities at fair value		$ 20,231	$ 23,012

[1] All mortgage-backed securities are guaranteed by U.S. government agencies or Government-sponsored entities.