Accumulated Other Comprehensive Income (Loss) (''AOCI'') - Amount Reclassified from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Amount Reclassified from AOCI
Gains on sale of securities	$ 347		$ 527
Interest income on taxable securities	2,829	$ 1,554	5,603	$ 3,157
Income tax expense	(4,377)	(2,690)	(8,103)	(5,120)
Net income	7,295	4,477	13,401	8,615
Amount Reclassified from AOCI
Amount Reclassified from AOCI
Net of tax	218	(22)	303	(63)
Unrealized Gains on Available-for-Sale Securities and I/O Strips
Amount Reclassified from AOCI
Net of tax	201		306
Unrealized Gains on Available-for-Sale Securities and I/O Strips | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Gains on sale of securities	347		527
Income tax expense	(146)		(221)
Net income	201		306
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity
Amount Reclassified from AOCI
Net of tax	44	8	52	16
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Interest income on taxable securities	76	14	90	28
Income tax expense	(32)	(6)	(38)	(12)
Net income	44	8	52	16
Defined Benefit Pension Plan Items
Amount Reclassified from AOCI
Net of tax	(27)	(30)	(55)	(79)
Defined Benefit Pension Plan Items | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	(47)	(52)	(94)	(136)
Income tax benefit	20	22	39	57
Net of tax	(27)	(30)	(55)	(79)
Prior transition obligation | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	13	44	26	56
Actuarial losses | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	$ (60)	$ (96)	$ (120)	$ (192)