Derivative and Hedging Activities (Interest Rate Derivatives) (Details) ₩ in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 KRW (₩)
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	70.00%	70.00%
Consolidated Subsidiaries Interest Rate Swap 3 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 50,000
Derivative, Fixed Interest Rate	3.02%	3.02%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	4.62%	4.62%
Derivative, Maturity Date	Mar. 01, 2023
Derivative, Effective Date	Mar. 01, 2019
Consolidated Subsidiaries Interest Rate Swap 3 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Unsecured Debt	$ 250,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	4.27%	4.27%
Derivative, Upper Range of Effective Rate, Variable Rate	4.92%	4.92%
Consolidated Subsidiaries Interest Rate Swap 3 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 3 Primary Line of Credit Swapped Portion [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one-month LIBOR
Consolidated Subsidiaries Interest Rate Swap 4 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 100,000
Derivative, Fixed Interest Rate	2.14%	2.14%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	3.74%	3.74%
Derivative, Maturity Date	Feb. 01, 2022
Unsecured Debt	$ 300,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	3.39%	3.39%
Derivative, Upper Range of Effective Rate, Variable Rate	4.04%	4.04%
Consolidated Subsidiaries Interest Rate Swap 4 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 5 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 100,000
Derivative, Fixed Interest Rate	2.14%	2.14%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	3.74%	3.74%
Derivative, Maturity Date	Feb. 01, 2022
Unsecured Debt	$ 300,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	3.39%	3.39%
Derivative, Upper Range of Effective Rate, Variable Rate	4.04%	4.04%
Consolidated Subsidiaries Interest Rate Swap 5 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 6 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 50,000
Derivative, Fixed Interest Rate	2.14%	2.14%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	3.74%	3.74%
Derivative, Maturity Date	Feb. 01, 2022
Unsecured Debt	$ 300,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	3.39%	3.39%
Derivative, Upper Range of Effective Rate, Variable Rate	4.04%	4.04%
Consolidated Subsidiaries Interest Rate Swap 6 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 7 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 50,000
Derivative, Fixed Interest Rate	2.14%	2.14%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	3.74%	3.74%
Derivative, Maturity Date	Feb. 01, 2022
Unsecured Debt	$ 300,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	3.39%	3.39%
Derivative, Upper Range of Effective Rate, Variable Rate	4.04%	4.04%
Consolidated Subsidiaries Interest Rate Swap 7 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 13 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 125,000
Derivative, Fixed Interest Rate	3.02%	3.02%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	4.62%	4.62%
Derivative, Maturity Date	Mar. 01, 2023
Derivative, Effective Date	Mar. 01, 2019
Unsecured Debt	$ 250,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	4.27%	4.27%
Derivative, Upper Range of Effective Rate, Variable Rate	4.92%	4.92%
Consolidated Subsidiaries Interest Rate Swap 13 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one-month LIBOR
Consolidated Subsidiaries Interest Rate Swap 12 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 75,000
Derivative, Fixed Interest Rate	3.02%	3.02%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	4.62%	4.62%
Derivative, Maturity Date	Mar. 01, 2023
Derivative, Effective Date	Mar. 01, 2019
Unsecured Debt	$ 250,000
Derivative, Lower Range of Basis Spread, Variable Rate	1.25%	1.25%
Derivative, Higher Range of Basis Spread, Variable Rate	1.90%	1.90%
Derivative, Lower Range of Effective Rate, Variable Rate	4.27%	4.27%
Derivative, Upper Range of Effective Rate, Variable Rate	4.92%	4.92%
Consolidated Subsidiaries Interest Rate Swap 12 [Domain] | London Interbank Offered Rate (LIBOR) [Member]
Cash flow hedges of interest rate risk [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month LIBOR
Consolidated Subsidiaries Interest Rate Swap 8 [Domain]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%
Derivative, Notional Amount	$ 12,000
Derivative, Fixed Interest Rate	2.09%	2.09%
Derivative, Basis Spread on Variable Rate	1.40%	1.40%
Total Swapped Rate On Loan	3.49%	3.49%
Derivative, Maturity Date	Mar. 01, 2024
Unconsolidated Joint Ventures Interest Rate Swap 1 [Member]
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	50.10%	50.10%
Derivative, Notional Amount	$ 160,410
Derivative, Fixed Interest Rate	1.83%	1.83%
Derivative, Basis Spread on Variable Rate	1.75%	1.75%
Total Swapped Rate On Loan	3.58%	3.58%
Derivative, Maturity Date	Dec. 01, 2021
Unconsolidated Joint Ventures Interest Rate Swap 2 (Member)
Cash flow hedges of interest rate risk [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	34.30%	34.30%
Derivative, Notional Amount	$ 52,065	₩ 60,500,000
Derivative, Fixed Interest Rate	1.52%	1.52%
Derivative, Basis Spread on Variable Rate	1.60%	1.60%
Total Swapped Rate On Loan	3.12%	3.12%
Derivative, Maturity Date	Sep. 01, 2020
Swapped Foreign Currency Exchange Rate	1,162.0